aboutsummaryrefslogtreecommitdiffstats
path: root/gcc-4.8.1/libgo/go/exp/html/testdata/go1.html
blob: a782cc71d209163e9197263951dfd445cf29deeb (plain) 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237

<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">

  <title>Go 1 Release Notes - The Go Programming Language</title>

<link type="text/css" rel="stylesheet" href="/doc/style.css">
<script type="text/javascript" src="/doc/godocs.js"></script>

<link rel="search" type="application/opensearchdescription+xml" title="godoc" href="/opensearch.xml" />

<script type="text/javascript">
var _gaq = _gaq || [];
_gaq.push(["_setAccount", "UA-11222381-2"]);
_gaq.push(["_trackPageview"]);
</script>
</head>
<body>

<div id="topbar"><div class="container wide">

<form method="GET" action="/search">
<div id="menu">
<a href="/doc/">Documents</a>
<a href="/ref/">References</a>
<a href="/pkg/">Packages</a>
<a href="/project/">The Project</a>
<a href="/help/">Help</a>
<input type="text" id="search" name="q" class="inactive" value="Search">
</div>
<div id="heading"><a href="/">The Go Programming Language</a></div>
</form>

</div></div>

<div id="page" class="wide">


  <div id="plusone"><g:plusone size="small" annotation="none"></g:plusone></div>
  <h1>Go 1 Release Notes</h1>




<div id="nav"></div>




<h2 id="introduction">Introduction to Go 1</h2>

<p>
Go version 1, Go 1 for short, defines a language and a set of core libraries
that provide a stable foundation for creating reliable products, projects, and
publications.
</p>

<p>
The driving motivation for Go 1 is stability for its users. People should be able to
write Go programs and expect that they will continue to compile and run without
change, on a time scale of years, including in production environments such as
Google App Engine. Similarly, people should be able to write books about Go, be
able to say which version of Go the book is describing, and have that version
number still be meaningful much later.
</p>

<p>
Code that compiles in Go 1 should, with few exceptions, continue to compile and
run throughout the lifetime of that version, even as we issue updates and bug
fixes such as Go version 1.1, 1.2, and so on. Other than critical fixes, changes
made to the language and library for subsequent releases of Go 1 may
add functionality but will not break existing Go 1 programs.
<a href="go1compat.html">The Go 1 compatibility document</a>
explains the compatibility guidelines in more detail.
</p>

<p>
Go 1 is a representation of Go as it used today, not a wholesale rethinking of
the language. We avoided designing new features and instead focused on cleaning
up problems and inconsistencies and improving portability. There are a number
changes to the Go language and packages that we had considered for some time and
prototyped but not released primarily because they are significant and
backwards-incompatible. Go 1 was an opportunity to get them out, which is
helpful for the long term, but also means that Go 1 introduces incompatibilities
for old programs. Fortunately, the <code>go</code> <code>fix</code> tool can
automate much of the work needed to bring programs up to the Go 1 standard.
</p>

<p>
This document outlines the major changes in Go 1 that will affect programmers
updating existing code; its reference point is the prior release, r60 (tagged as
r60.3). It also explains how to update code from r60 to run under Go 1.
</p>

<h2 id="language">Changes to the language</h2>

<h3 id="append">Append</h3>

<p>
The <code>append</code> predeclared variadic function makes it easy to grow a slice
by adding elements to the end.
A common use is to add bytes to the end of a byte slice when generating output.
However, <code>append</code> did not provide a way to append a string to a <code>[]byte</code>,
which is another common case.
</p>

<pre><!--{{code "/doc/progs/go1.go" `/greeting := ..byte/` `/append.*hello/`}}
-->    greeting := []byte{}
    greeting = append(greeting, []byte(&#34;hello &#34;)...)</pre>

<p>
By analogy with the similar property of <code>copy</code>, Go 1
permits a string to be appended (byte-wise) directly to a byte
slice, reducing the friction between strings and byte slices.
The conversion is no longer necessary:
</p>

<pre><!--{{code "/doc/progs/go1.go" `/append.*world/`}}
-->    greeting = append(greeting, &#34;world&#34;...)</pre>

<p>
<em>Updating</em>:
This is a new feature, so existing code needs no changes.
</p>

<h3 id="close">Close</h3>

<p>
The <code>close</code> predeclared function provides a mechanism
for a sender to signal that no more values will be sent.
It is important to the implementation of <code>for</code> <code>range</code>
loops over channels and is helpful in other situations.
Partly by design and partly because of race conditions that can occur otherwise,
it is intended for use only by the goroutine sending on the channel,
not by the goroutine receiving data.
However, before Go 1 there was no compile-time checking that <code>close</code>
was being used correctly.
</p>

<p>
To close this gap, at least in part, Go 1 disallows <code>close</code> on receive-only channels.
Attempting to close such a channel is a compile-time error.
</p>

<pre>
    var c chan int
    var csend chan&lt;- int = c
    var crecv &lt;-chan int = c
    close(c)     // legal
    close(csend) // legal
    close(crecv) // illegal
</pre>

<p>
<em>Updating</em>:
Existing code that attempts to close a receive-only channel was
erroneous even before Go 1 and should be fixed.  The compiler will
now reject such code.
</p>

<h3 id="literals">Composite literals</h3>

<p>
In Go 1, a composite literal of array, slice, or map type can elide the
type specification for the elements' initializers if they are of pointer type.
All four of the initializations in this example are legal; the last one was illegal before Go 1.
</p>

<pre><!--{{code "/doc/progs/go1.go" `/type Date struct/` `/STOP/`}}
-->    type Date struct {
        month string
        day   int
    }
    <span class="comment">// Struct values, fully qualified; always legal.</span>
    holiday1 := []Date{
        Date{&#34;Feb&#34;, 14},
        Date{&#34;Nov&#34;, 11},
        Date{&#34;Dec&#34;, 25},
    }
    <span class="comment">// Struct values, type name elided; always legal.</span>
    holiday2 := []Date{
        {&#34;Feb&#34;, 14},
        {&#34;Nov&#34;, 11},
        {&#34;Dec&#34;, 25},
    }
    <span class="comment">// Pointers, fully qualified, always legal.</span>
    holiday3 := []*Date{
        &amp;Date{&#34;Feb&#34;, 14},
        &amp;Date{&#34;Nov&#34;, 11},
        &amp;Date{&#34;Dec&#34;, 25},
    }
    <span class="comment">// Pointers, type name elided; legal in Go 1.</span>
    holiday4 := []*Date{
        {&#34;Feb&#34;, 14},
        {&#34;Nov&#34;, 11},
        {&#34;Dec&#34;, 25},
    }</pre>

<p>
<em>Updating</em>:
This change has no effect on existing code, but the command
<code>gofmt</code> <code>-s</code> applied to existing source
will, among other things, elide explicit element types wherever permitted.
</p>


<h3 id="init">Goroutines during init</h3>

<p>
The old language defined that <code>go</code> statements executed during initialization created goroutines but that they did not begin to run until initialization of the entire program was complete.
This introduced clumsiness in many places and, in effect, limited the utility
of the <code>init</code> construct:
if it was possible for another package to use the library during initialization, the library
was forced to avoid goroutines.
This design was done for reasons of simplicity and safety but,
as our confidence in the language grew, it seemed unnecessary.
Running goroutines during initialization is no more complex or unsafe than running them during normal execution.
</p>

<p>
In Go 1, code that uses goroutines can be called from
<code>init</code> routines and global initialization expressions
without introducing a deadlock.
</p>

<pre><!--{{code "/doc/progs/go1.go" `/PackageGlobal/` `/^}/`}}
-->var PackageGlobal int

func init() {
    c := make(chan int)
    go initializationFunction(c)
    PackageGlobal = &lt;-c
}</pre>

<p>
<em>Updating</em>:
This is a new feature, so existing code needs no changes,
although it's possible that code that depends on goroutines not starting before <code>main</code> will break.
There was no such code in the standard repository.
</p>

<h3 id="rune">The rune type</h3>

<p>
The language spec allows the <code>int</code> type to be 32 or 64 bits wide, but current implementations set <code>int</code> to 32 bits even on 64-bit platforms.
It would be preferable to have <code>int</code> be 64 bits on 64-bit platforms.
(There are important consequences for indexing large slices.)
However, this change would waste space when processing Unicode characters with
the old language because the <code>int</code> type was also used to hold Unicode code points: each code point would waste an extra 32 bits of storage if <code>int</code> grew from 32 bits to 64.
</p>

<p>
To make changing to 64-bit <code>int</code> feasible,
Go 1 introduces a new basic type, <code>rune</code>, to represent
individual Unicode code points.
It is an alias for <code>int32</code>, analogous to <code>byte</code>
as an alias for <code>uint8</code>.
</p>

<p>
Character literals such as <code>'a'</code>, <code>'語'</code>, and <code>'\u0345'</code>
now have default type <code>rune</code>,
analogous to <code>1.0</code> having default type <code>float64</code>.
A variable initialized to a character constant will therefore
have type <code>rune</code> unless otherwise specified.
</p>

<p>
Libraries have been updated to use <code>rune</code> rather than <code>int</code>
when appropriate. For instance, the functions <code>unicode.ToLower</code> and
relatives now take and return a <code>rune</code>.
</p>

<pre><!--{{code "/doc/progs/go1.go" `/STARTRUNE/` `/ENDRUNE/`}}
-->    delta := &#39;δ&#39; <span class="comment">// delta has type rune.</span>
    var DELTA rune
    DELTA = unicode.ToUpper(delta)
    epsilon := unicode.ToLower(DELTA + 1)
    if epsilon != &#39;δ&#39;+1 {
        log.Fatal(&#34;inconsistent casing for Greek&#34;)
    }</pre>

<p>
<em>Updating</em>:
Most source code will be unaffected by this because the type inference from
<code>:=</code> initializers introduces the new type silently, and it propagates
from there.
Some code may get type errors that a trivial conversion will resolve.
</p>

<h3 id="error">The error type</h3>

<p>
Go 1 introduces a new built-in type, <code>error</code>, which has the following definition:
</p>

<pre>
    type error interface {
        Error() string
    }
</pre>

<p>
Since the consequences of this type are all in the package library,
it is discussed <a href="#errors">below</a>.
</p>

<h3 id="delete">Deleting from maps</h3>

<p>
In the old language, to delete the entry with key <code>k</code> from map <code>m</code>, one wrote the statement,
</p>

<pre>
    m[k] = value, false
</pre>

<p>
This syntax was a peculiar special case, the only two-to-one assignment.
It required passing a value (usually ignored) that is evaluated but discarded,
plus a boolean that was nearly always the constant <code>false</code>.
It did the job but was odd and a point of contention.
</p>

<p>
In Go 1, that syntax has gone; instead there is a new built-in
function, <code>delete</code>.  The call
</p>

<pre><!--{{code "/doc/progs/go1.go" `/delete\(m, k\)/`}}
-->    delete(m, k)</pre>

<p>
will delete the map entry retrieved by the expression <code>m[k]</code>.
There is no return value. Deleting a non-existent entry is a no-op.
</p>

<p>
<em>Updating</em>:
Running <code>go</code> <code>fix</code> will convert expressions of the form <code>m[k] = value,
false</code> into <code>delete(m, k)</code> when it is clear that
the ignored value can be safely discarded from the program and
<code>false</code> refers to the predefined boolean constant.
The fix tool
will flag other uses of the syntax for inspection by the programmer.
</p>

<h3 id="iteration">Iterating in maps</h3>

<p>
The old language specification did not define the order of iteration for maps,
and in practice it differed across hardware platforms.
This caused tests that iterated over maps to be fragile and non-portable, with the
unpleasant property that a test might always pass on one machine but break on another.
</p>

<p>
In Go 1, the order in which elements are visited when iterating
over a map using a <code>for</code> <code>range</code> statement
is defined to be unpredictable, even if the same loop is run multiple
times with the same map.
Code should not assume that the elements are visited in any particular order.
</p>

<p>
This change means that code that depends on iteration order is very likely to break early and be fixed long before it becomes a problem.
Just as important, it allows the map implementation to ensure better map balancing even when programs are using range loops to select an element from a map.
</p>

<pre><!--{{code "/doc/progs/go1.go" `/Sunday/` `/^	}/`}}
-->    m := map[string]int{&#34;Sunday&#34;: 0, &#34;Monday&#34;: 1}
    for name, value := range m {
        <span class="comment">// This loop should not assume Sunday will be visited first.</span>
        f(name, value)
    }</pre>

<p>
<em>Updating</em>:
This is one change where tools cannot help.  Most existing code
will be unaffected, but some programs may break or misbehave; we
recommend manual checking of all range statements over maps to
verify they do not depend on iteration order. There were a few such
examples in the standard repository; they have been fixed.
Note that it was already incorrect to depend on the iteration order, which
was unspecified. This change codifies the unpredictability.
</p>

<h3 id="multiple_assignment">Multiple assignment</h3>

<p>
The language specification has long guaranteed that in assignments
the right-hand-side expressions are all evaluated before any left-hand-side expressions are assigned.
To guarantee predictable behavior,
Go 1 refines the specification further.
</p>

<p>
If the left-hand side of the assignment
statement contains expressions that require evaluation, such as
function calls or array indexing operations, these will all be done
using the usual left-to-right rule before any variables are assigned
their value.  Once everything is evaluated, the actual assignments
proceed in left-to-right order.
</p>

<p>
These examples illustrate the behavior.
</p>

<pre><!--{{code "/doc/progs/go1.go" `/sa :=/` `/then sc.0. = 2/`}}
-->    sa := []int{1, 2, 3}
    i := 0
    i, sa[i] = 1, 2 <span class="comment">// sets i = 1, sa[0] = 2</span>

    sb := []int{1, 2, 3}
    j := 0
    sb[j], j = 2, 1 <span class="comment">// sets sb[0] = 2, j = 1</span>

    sc := []int{1, 2, 3}
    sc[0], sc[0] = 1, 2 <span class="comment">// sets sc[0] = 1, then sc[0] = 2 (so sc[0] = 2 at end)</span></pre>

<p>
<em>Updating</em>:
This is one change where tools cannot help, but breakage is unlikely.
No code in the standard repository was broken by this change, and code
that depended on the previous unspecified behavior was already incorrect.
</p>

<h3 id="shadowing">Returns and shadowed variables</h3>

<p>
A common mistake is to use <code>return</code> (without arguments) after an assignment to a variable that has the same name as a result variable but is not the same variable.
This situation is called <em>shadowing</em>: the result variable has been shadowed by another variable with the same name declared in an inner scope.
</p>

<p>
In functions with named return values,
the Go 1 compilers disallow return statements without arguments if any of the named return values is shadowed at the point of the return statement.
(It isn't part of the specification, because this is one area we are still exploring;
the situation is analogous to the compilers rejecting functions that do not end with an explicit return statement.)
</p>

<p>
This function implicitly returns a shadowed return value and will be rejected by the compiler:
</p>

<pre>
    func Bug() (i, j, k int) {
        for i = 0; i &lt; 5; i++ {
            for j := 0; j &lt; 5; j++ { // Redeclares j.
                k += i*j
                if k > 100 {
                    return // Rejected: j is shadowed here.
                }
            }
        }
        return // OK: j is not shadowed here.
    }
</pre>

<p>
<em>Updating</em>:
Code that shadows return values in this way will be rejected by the compiler and will need to be fixed by hand.
The few cases that arose in the standard repository were mostly bugs.
</p>

<h3 id="unexported">Copying structs with unexported fields</h3>

<p>
The old language did not allow a package to make a copy of a struct value containing unexported fields belonging to a different package.
There was, however, a required exception for a method receiver;
also, the implementations of <code>copy</code> and <code>append</code> have never honored the restriction.
</p>

<p>
Go 1 will allow packages to copy struct values containing unexported fields from other packages.
Besides resolving the inconsistency,
this change admits a new kind of API: a package can return an opaque value without resorting to a pointer or interface.
The new implementations of <code>time.Time</code> and
<code>reflect.Value</code> are examples of types taking advantage of this new property.
</p>

<p>
As an example, if package <code>p</code> includes the definitions,
</p>

<pre>
    type Struct struct {
        Public int
        secret int
    }
    func NewStruct(a int) Struct {  // Note: not a pointer.
        return Struct{a, f(a)}
    }
    func (s Struct) String() string {
        return fmt.Sprintf("{%d (secret %d)}", s.Public, s.secret)
    }
</pre>

<p>
a package that imports <code>p</code> can assign and copy values of type
<code>p.Struct</code> at will.
Behind the scenes the unexported fields will be assigned and copied just
as if they were exported,
but the client code will never be aware of them. The code
</p>

<pre>
    import "p"

    myStruct := p.NewStruct(23)
    copyOfMyStruct := myStruct
    fmt.Println(myStruct, copyOfMyStruct)
</pre>

<p>
will show that the secret field of the struct has been copied to the new value.
</p>

<p>
<em>Updating</em>:
This is a new feature, so existing code needs no changes.
</p>

<h3 id="equality">Equality</h3>

<p>
Before Go 1, the language did not define equality on struct and array values.
This meant,
among other things, that structs and arrays could not be used as map keys.
On the other hand, Go did define equality on function and map values.
Function equality was problematic in the presence of closures
(when are two closures equal?)
while map equality compared pointers, not the maps' content, which was usually
not what the user would want.
</p>

<p>
Go 1 addressed these issues.
First, structs and arrays can be compared for equality and inequality
(<code>==</code> and <code>!=</code>),
and therefore be used as map keys,
provided they are composed from elements for which equality is also defined,
using element-wise comparison.
</p>

<pre><!--{{code "/doc/progs/go1.go" `/type Day struct/` `/Printf/`}}
-->    type Day struct {
        long  string
        short string
    }
    Christmas := Day{&#34;Christmas&#34;, &#34;XMas&#34;}
    Thanksgiving := Day{&#34;Thanksgiving&#34;, &#34;Turkey&#34;}
    holiday := map[Day]bool{
        Christmas:    true,
        Thanksgiving: true,
    }
    fmt.Printf(&#34;Christmas is a holiday: %t\n&#34;, holiday[Christmas])</pre>

<p>
Second, Go 1 removes the definition of equality for function values,
except for comparison with <code>nil</code>.
Finally, map equality is gone too, also except for comparison with <code>nil</code>.
</p>

<p>
Note that equality is still undefined for slices, for which the
calculation is in general infeasible.  Also note that the ordered
comparison operators (<code>&lt;</code> <code>&lt;=</code>
<code>&gt;</code> <code>&gt;=</code>) are still undefined for
structs and arrays.

<p>
<em>Updating</em>:
Struct and array equality is a new feature, so existing code needs no changes.
Existing code that depends on function or map equality will be
rejected by the compiler and will need to be fixed by hand.
Few programs will be affected, but the fix may require some
redesign.
</p>

<h2 id="packages">The package hierarchy</h2>

<p>
Go 1 addresses many deficiencies in the old standard library and
cleans up a number of packages, making them more internally consistent
and portable.
</p>

<p>
This section describes how the packages have been rearranged in Go 1.
Some have moved, some have been renamed, some have been deleted.
New packages are described in later sections.
</p>

<h3 id="hierarchy">The package hierarchy</h3>

<p>
Go 1 has a rearranged package hierarchy that groups related items
into subdirectories. For instance, <code>utf8</code> and
<code>utf16</code> now occupy subdirectories of <code>unicode</code>.
Also, <a href="#subrepo">some packages</a> have moved into
subrepositories of
<a href="http://code.google.com/p/go"><code>code.google.com/p/go</code></a>
while <a href="#deleted">others</a> have been deleted outright.
</p>

<table class="codetable" frame="border" summary="Moved packages">
<colgroup align="left" width="60%"></colgroup>
<colgroup align="left" width="40%"></colgroup>
<tr>
<th align="left">Old path</th>
<th align="left">New path</th>
</tr>
<tr>
<td colspan="2"><hr></td>
</tr>
<tr><td>asn1</td> <td>encoding/asn1</td></tr>
<tr><td>csv</td> <td>encoding/csv</td></tr>
<tr><td>gob</td> <td>encoding/gob</td></tr>
<tr><td>json</td> <td>encoding/json</td></tr>
<tr><td>xml</td> <td>encoding/xml</td></tr>
<tr>
<td colspan="2"><hr></td>
</tr>
<tr><td>exp/template/html</td> <td>html/template</td></tr>
<tr>
<td colspan="2"><hr></td>
</tr>
<tr><td>big</td> <td>math/big</td></tr>
<tr><td>cmath</td> <td>math/cmplx</td></tr>
<tr><td>rand</td> <td>math/rand</td></tr>
<tr>
<td colspan="2"><hr></td>
</tr>
<tr><td>http</td> <td>net/http</td></tr>
<tr><td>http/cgi</td> <td>net/http/cgi</td></tr>
<tr><td>http/fcgi</td> <td>net/http/fcgi</td></tr>
<tr><td>http/httptest</td> <td>net/http/httptest</td></tr>
<tr><td>http/pprof</td> <td>net/http/pprof</td></tr>
<tr><td>mail</td> <td>net/mail</td></tr>
<tr><td>rpc</td> <td>net/rpc</td></tr>
<tr><td>rpc/jsonrpc</td> <td>net/rpc/jsonrpc</td></tr>
<tr><td>smtp</td> <td>net/smtp</td></tr>
<tr><td>url</td> <td>net/url</td></tr>
<tr>
<td colspan="2"><hr></td>
</tr>
<tr><td>exec</td> <td>os/exec</td></tr>
<tr>
<td colspan="2"><hr></td>
</tr>
<tr><td>scanner</td> <td>text/scanner</td></tr>
<tr><td>tabwriter</td> <td>text/tabwriter</td></tr>
<tr><td>template</td> <td>text/template</td></tr>
<tr><td>template/parse</td> <td>text/template/parse</td></tr>
<tr>
<td colspan="2"><hr></td>
</tr>
<tr><td>utf8</td> <td>unicode/utf8</td></tr>
<tr><td>utf16</td> <td>unicode/utf16</td></tr>
</table>

<p>
Note that the package names for the old <code>cmath</code> and
<code>exp/template/html</code> packages have changed to <code>cmplx</code>
and <code>template</code>.
</p>

<p>
<em>Updating</em>:
Running <code>go</code> <code>fix</code> will update all imports and package renames for packages that
remain inside the standard repository.  Programs that import packages
that are no longer in the standard repository will need to be edited
by hand.
</p>

<h3 id="exp">The package tree exp</h3>

<p>
Because they are not standardized, the packages under the <code>exp</code> directory will not be available in the
standard Go 1 release distributions, although they will be available in source code form
in <a href="http://code.google.com/p/go/">the repository</a> for
developers who wish to use them.
</p>

<p>
Several packages have moved under <code>exp</code> at the time of Go 1's release:
</p>

<ul>
<li><code>ebnf</code></li>
<li><code>html</code><sup>&#8224;</sup></li>
<li><code>go/types</code></li>
</ul>

<p>
(<sup>&#8224;</sup>The <code>EscapeString</code> and <code>UnescapeString</code> types remain
in package <code>html</code>.)
</p>

<p>
All these packages are available under the same names, with the prefix <code>exp/</code>: <code>exp/ebnf</code> etc.
</p>

<p>
Also, the <code>utf8.String</code> type has been moved to its own package, <code>exp/utf8string</code>.
</p>

<p>
Finally, the <code>gotype</code> command now resides in <code>exp/gotype</code>, while
<code>ebnflint</code> is now in <code>exp/ebnflint</code>.
If they are installed, they now reside in <code>$GOROOT/bin/tool</code>.
</p>

<p>
<em>Updating</em>:
Code that uses packages in <code>exp</code> will need to be updated by hand,
or else compiled from an installation that has <code>exp</code> available.
The <code>go</code> <code>fix</code> tool or the compiler will complain about such uses.
</p>

<h3 id="old">The package tree old</h3>

<p>
Because they are deprecated, the packages under the <code>old</code> directory will not be available in the
standard Go 1 release distributions, although they will be available in source code form for
developers who wish to use them.
</p>

<p>
The packages in their new locations are:
</p>

<ul>
<li><code>old/netchan</code></li>
<li><code>old/regexp</code></li>
<li><code>old/template</code></li>
</ul>

<p>
<em>Updating</em>:
Code that uses packages now in <code>old</code> will need to be updated by hand,
or else compiled from an installation that has <code>old</code> available.
The <code>go</code> <code>fix</code> tool will warn about such uses.
</p>

<h3 id="deleted">Deleted packages</h3>

<p>
Go 1 deletes several packages outright:
</p>

<ul>
<li><code>container/vector</code></li>
<li><code>exp/datafmt</code></li>
<li><code>go/typechecker</code></li>
<li><code>try</code></li>
</ul>

<p>
and also the command <code>gotry</code>.
</p>

<p>
<em>Updating</em>:
Code that uses <code>container/vector</code> should be updated to use
slices directly.  See
<a href="http://code.google.com/p/go-wiki/wiki/SliceTricks">the Go
Language Community Wiki</a> for some suggestions.
Code that uses the other packages (there should be almost zero) will need to be rethought.
</p>

<h3 id="subrepo">Packages moving to subrepositories</h3>

<p>
Go 1 has moved a number of packages into other repositories, usually sub-repositories of
<a href="http://code.google.com/p/go/">the main Go repository</a>.
This table lists the old and new import paths:

<table class="codetable" frame="border" summary="Sub-repositories">
<colgroup align="left" width="40%"></colgroup>
<colgroup align="left" width="60%"></colgroup>
<tr>
<th align="left">Old</th>
<th align="left">New</th>
</tr>
<tr>
<td colspan="2"><hr></td>
</tr>
<tr><td>crypto/bcrypt</td> <td>code.google.com/p/go.crypto/bcrypt</tr>
<tr><td>crypto/blowfish</td> <td>code.google.com/p/go.crypto/blowfish</tr>
<tr><td>crypto/cast5</td> <td>code.google.com/p/go.crypto/cast5</tr>
<tr><td>crypto/md4</td> <td>code.google.com/p/go.crypto/md4</tr>
<tr><td>crypto/ocsp</td> <td>code.google.com/p/go.crypto/ocsp</tr>
<tr><td>crypto/openpgp</td> <td>code.google.com/p/go.crypto/openpgp</tr>
<tr><td>crypto/openpgp/armor</td> <td>code.google.com/p/go.crypto/openpgp/armor</tr>
<tr><td>crypto/openpgp/elgamal</td> <td>code.google.com/p/go.crypto/openpgp/elgamal</tr>
<tr><td>crypto/openpgp/errors</td> <td>code.google.com/p/go.crypto/openpgp/errors</tr>
<tr><td>crypto/openpgp/packet</td> <td>code.google.com/p/go.crypto/openpgp/packet</tr>
<tr><td>crypto/openpgp/s2k</td> <td>code.google.com/p/go.crypto/openpgp/s2k</tr>
<tr><td>crypto/ripemd160</td> <td>code.google.com/p/go.crypto/ripemd160</tr>
<tr><td>crypto/twofish</td> <td>code.google.com/p/go.crypto/twofish</tr>
<tr><td>crypto/xtea</td> <td>code.google.com/p/go.crypto/xtea</tr>
<tr><td>exp/ssh</td> <td>code.google.com/p/go.crypto/ssh</tr>
<tr>
<td colspan="2"><hr></td>
</tr>
<tr><td>image/bmp</td> <td>code.google.com/p/go.image/bmp</tr>
<tr><td>image/tiff</td> <td>code.google.com/p/go.image/tiff</tr>
<tr>
<td colspan="2"><hr></td>
</tr>
<tr><td>net/dict</td> <td>code.google.com/p/go.net/dict</tr>
<tr><td>net/websocket</td> <td>code.google.com/p/go.net/websocket</tr>
<tr><td>exp/spdy</td> <td>code.google.com/p/go.net/spdy</tr>
<tr>
<td colspan="2"><hr></td>
</tr>
<tr><td>encoding/git85</td> <td>code.google.com/p/go.codereview/git85</tr>
<tr><td>patch</td> <td>code.google.com/p/go.codereview/patch</tr>
<tr>
<td colspan="2"><hr></td>
</tr>
<tr><td>exp/wingui</td> <td>code.google.com/p/gowingui</tr>
</table>

<p>
<em>Updating</em>:
Running <code>go</code> <code>fix</code> will update imports of these packages to use the new import paths.
Installations that depend on these packages will need to install them using
a <code>go get</code> command.
</p>

<h2 id="major">Major changes to the library</h2>

<p>
This section describes significant changes to the core libraries, the ones that
affect the most programs.
</p>

<h3 id="errors">The error type and errors package</h3>

<p>
The placement of <code>os.Error</code> in package <code>os</code> is mostly historical: errors first came up when implementing package <code>os</code>, and they seemed system-related at the time.
Since then it has become clear that errors are more fundamental than the operating system.  For example, it would be nice to use <code>Errors</code> in packages that <code>os</code> depends on, like <code>syscall</code>.
Also, having <code>Error</code> in <code>os</code> introduces many dependencies on <code>os</code> that would otherwise not exist.
</p>

<p>
Go 1 solves these problems by introducing a built-in <code>error</code> interface type and a separate <code>errors</code> package (analogous to <code>bytes</code> and <code>strings</code>) that contains utility functions.
It replaces <code>os.NewError</code> with
<a href="/pkg/errors/#New"><code>errors.New</code></a>,
giving errors a more central place in the environment.
</p>

<p>
So the widely-used <code>String</code> method does not cause accidental satisfaction
of the <code>error</code> interface, the <code>error</code> interface uses instead
the name <code>Error</code> for that method:
</p>

<pre>
    type error interface {
        Error() string
    }
</pre>

<p>
The <code>fmt</code> library automatically invokes <code>Error</code>, as it already
does for <code>String</code>, for easy printing of error values.
</p>

<pre><!--{{code "/doc/progs/go1.go" `/START ERROR EXAMPLE/` `/END ERROR EXAMPLE/`}}
-->type SyntaxError struct {
    File    string
    Line    int
    Message string
}

func (se *SyntaxError) Error() string {
    return fmt.Sprintf(&#34;%s:%d: %s&#34;, se.File, se.Line, se.Message)
}</pre>

<p>
All standard packages have been updated to use the new interface; the old <code>os.Error</code> is gone.
</p>

<p>
A new package, <a href="/pkg/errors/"><code>errors</code></a>, contains the function
</p>

<pre>
func New(text string) error
</pre>

<p>
to turn a string into an error. It replaces the old <code>os.NewError</code>.
</p>

<pre><!--{{code "/doc/progs/go1.go" `/ErrSyntax/`}}
-->    var ErrSyntax = errors.New(&#34;syntax error&#34;)</pre>
		
<p>
<em>Updating</em>:
Running <code>go</code> <code>fix</code> will update almost all code affected by the change.
Code that defines error types with a <code>String</code> method will need to be updated
by hand to rename the methods to <code>Error</code>.
</p>

<h3 id="errno">System call errors</h3>

<p>
The old <code>syscall</code> package, which predated <code>os.Error</code>
(and just about everything else),
returned errors as <code>int</code> values.
In turn, the <code>os</code> package forwarded many of these errors, such
as <code>EINVAL</code>, but using a different set of errors on each platform.
This behavior was unpleasant and unportable.
</p>

<p>
In Go 1, the
<a href="/pkg/syscall/"><code>syscall</code></a>
package instead returns an <code>error</code> for system call errors.
On Unix, the implementation is done by a
<a href="/pkg/syscall/#Errno"><code>syscall.Errno</code></a> type
that satisfies <code>error</code> and replaces the old <code>os.Errno</code>.
</p>

<p>
The changes affecting <code>os.EINVAL</code> and relatives are
described <a href="#os">elsewhere</a>.

<p>
<em>Updating</em>:
Running <code>go</code> <code>fix</code> will update almost all code affected by the change.
Regardless, most code should use the <code>os</code> package
rather than <code>syscall</code> and so will be unaffected.
</p>

<h3 id="time">Time</h3>

<p>
Time is always a challenge to support well in a programming language.
The old Go <code>time</code> package had <code>int64</code> units, no
real type safety,
and no distinction between absolute times and durations.
</p>

<p>
One of the most sweeping changes in the Go 1 library is therefore a
complete redesign of the
<a href="/pkg/time/"><code>time</code></a> package.
Instead of an integer number of nanoseconds as an <code>int64</code>,
and a separate <code>*time.Time</code> type to deal with human
units such as hours and years,
there are now two fundamental types:
<a href="/pkg/time/#Time"><code>time.Time</code></a>
(a value, so the <code>*</code> is gone), which represents a moment in time;
and <a href="/pkg/time/#Duration"><code>time.Duration</code></a>,
which represents an interval.
Both have nanosecond resolution.
A <code>Time</code> can represent any time into the ancient
past and remote future, while a <code>Duration</code> can
span plus or minus only about 290 years.
There are methods on these types, plus a number of helpful
predefined constant durations such as <code>time.Second</code>.
</p>

<p>
Among the new methods are things like
<a href="/pkg/time/#Time.Add"><code>Time.Add</code></a>,
which adds a <code>Duration</code> to a <code>Time</code>, and
<a href="/pkg/time/#Time.Sub"><code>Time.Sub</code></a>,
which subtracts two <code>Times</code> to yield a <code>Duration</code>.
</p>

<p>
The most important semantic change is that the Unix epoch (Jan 1, 1970) is now
relevant only for those functions and methods that mention Unix:
<a href="/pkg/time/#Unix"><code>time.Unix</code></a>
and the <a href="/pkg/time/#Time.Unix"><code>Unix</code></a>
and <a href="/pkg/time/#Time.UnixNano"><code>UnixNano</code></a> methods
of the <code>Time</code> type.
In particular,
<a href="/pkg/time/#Now"><code>time.Now</code></a>
returns a <code>time.Time</code> value rather than, in the old
API, an integer nanosecond count since the Unix epoch.
</p>

<pre><!--{{code "/doc/progs/go1.go" `/sleepUntil/` `/^}/`}}
--><span class="comment">// sleepUntil sleeps until the specified time. It returns immediately if it&#39;s too late.</span>
func sleepUntil(wakeup time.Time) {
    now := time.Now() <span class="comment">// A Time.</span>
    if !wakeup.After(now) {
        return
    }
    delta := wakeup.Sub(now) <span class="comment">// A Duration.</span>
    fmt.Printf(&#34;Sleeping for %.3fs\n&#34;, delta.Seconds())
    time.Sleep(delta)
}</pre>

<p>
The new types, methods, and constants have been propagated through
all the standard packages that use time, such as <code>os</code> and
its representation of file time stamps.
</p>

<p>
<em>Updating</em>:
The <code>go</code> <code>fix</code> tool will update many uses of the old <code>time</code> package to use the new
types and methods, although it does not replace values such as <code>1e9</code>
representing nanoseconds per second.
Also, because of type changes in some of the values that arise,
some of the expressions rewritten by the fix tool may require
further hand editing; in such cases the rewrite will include
the correct function or method for the old functionality, but
may have the wrong type or require further analysis.
</p>

<h2 id="minor">Minor changes to the library</h2>

<p>
This section describes smaller changes, such as those to less commonly
used packages or that affect
few programs beyond the need to run <code>go</code> <code>fix</code>.
This category includes packages that are new in Go 1.
Collectively they improve portability, regularize behavior, and
make the interfaces more modern and Go-like.
</p>

<h3 id="archive_zip">The archive/zip package</h3>

<p>
In Go 1, <a href="/pkg/archive/zip/#Writer"><code>*zip.Writer</code></a> no
longer has a <code>Write</code> method. Its presence was a mistake.
</p>

<p>
<em>Updating</em>:
What little code is affected will be caught by the compiler and must be updated by hand.
</p>

<h3 id="bufio">The bufio package</h3>

<p>
In Go 1, <a href="/pkg/bufio/#NewReaderSize"><code>bufio.NewReaderSize</code></a>
and
<a href="/pkg/bufio/#NewWriterSize"><code>bufio.NewWriterSize</code></a>
functions no longer return an error for invalid sizes.
If the argument size is too small or invalid, it is adjusted.
</p>

<p>
<em>Updating</em>:
Running <code>go</code> <code>fix</code> will update calls that assign the error to _.
Calls that aren't fixed will be caught by the compiler and must be updated by hand.
</p>

<h3 id="compress">The compress/flate, compress/gzip and compress/zlib packages</h3>

<p>
In Go 1, the <code>NewWriterXxx</code> functions in
<a href="/pkg/compress/flate"><code>compress/flate</code></a>,
<a href="/pkg/compress/gzip"><code>compress/gzip</code></a> and
<a href="/pkg/compress/zlib"><code>compress/zlib</code></a>
all return <code>(*Writer, error)</code> if they take a compression level,
and <code>*Writer</code> otherwise. Package <code>gzip</code>'s
<code>Compressor</code> and <code>Decompressor</code> types have been renamed
to <code>Writer</code> and <code>Reader</code>. Package <code>flate</code>'s
<code>WrongValueError</code> type has been removed.
</p>

<p>
<em>Updating</em>
Running <code>go</code> <code>fix</code> will update old names and calls that assign the error to _.
Calls that aren't fixed will be caught by the compiler and must be updated by hand.
</p>

<h3 id="crypto_aes_des">The crypto/aes and crypto/des packages</h3>

<p>
In Go 1, the <code>Reset</code> method has been removed. Go does not guarantee
that memory is not copied and therefore this method was misleading.
</p>

<p>
The cipher-specific types <code>*aes.Cipher</code>, <code>*des.Cipher</code>,
and <code>*des.TripleDESCipher</code> have been removed in favor of
<code>cipher.Block</code>.
</p>

<p>
<em>Updating</em>:
Remove the calls to Reset. Replace uses of the specific cipher types with
cipher.Block.
</p>

<h3 id="crypto_elliptic">The crypto/elliptic package</h3>

<p>
In Go 1, <a href="/pkg/crypto/elliptic/#Curve"><code>elliptic.Curve</code></a>
has been made an interface to permit alternative implementations. The curve
parameters have been moved to the
<a href="/pkg/crypto/elliptic/#CurveParams"><code>elliptic.CurveParams</code></a>
structure.
</p>

<p>
<em>Updating</em>:
Existing users of <code>*elliptic.Curve</code> will need to change to
simply <code>elliptic.Curve</code>. Calls to <code>Marshal</code>,
<code>Unmarshal</code> and <code>GenerateKey</code> are now functions
in <code>crypto/elliptic</code> that take an <code>elliptic.Curve</code>
as their first argument.
</p>

<h3 id="crypto_hmac">The crypto/hmac package</h3>

<p>
In Go 1, the hash-specific functions, such as <code>hmac.NewMD5</code>, have
been removed from <code>crypto/hmac</code>. Instead, <code>hmac.New</code> takes
a function that returns a <code>hash.Hash</code>, such as <code>md5.New</code>.
</p>

<p>
<em>Updating</em>:
Running <code>go</code> <code>fix</code> will perform the needed changes.
</p>

<h3 id="crypto_x509">The crypto/x509 package</h3>

<p>
In Go 1, the
<a href="/pkg/crypto/x509/#CreateCertificate"><code>CreateCertificate</code></a>
and
<a href="/pkg/crypto/x509/#CreateCRL"><code>CreateCRL</code></a>
functions in <code>crypto/x509</code> have been altered to take an
<code>interface{}</code> where they previously took a <code>*rsa.PublicKey</code>
or <code>*rsa.PrivateKey</code>. This will allow other public key algorithms
to be implemented in the future.
</p>

<p>
<em>Updating</em>:
No changes will be needed.
</p>

<h3 id="encoding_binary">The encoding/binary package</h3>

<p>
In Go 1, the <code>binary.TotalSize</code> function has been replaced by
<a href="/pkg/encoding/binary/#Size"><code>Size</code></a>,
which takes an <code>interface{}</code> argument rather than
a <code>reflect.Value</code>.
</p>

<p>
<em>Updating</em>:
What little code is affected will be caught by the compiler and must be updated by hand.
</p>

<h3 id="encoding_xml">The encoding/xml package</h3>

<p>
In Go 1, the <a href="/pkg/encoding/xml/"><code>xml</code></a> package
has been brought closer in design to the other marshaling packages such
as <a href="/pkg/encoding/gob/"><code>encoding/gob</code></a>.
</p>

<p>
The old <code>Parser</code> type is renamed
<a href="/pkg/encoding/xml/#Decoder"><code>Decoder</code></a> and has a new
<a href="/pkg/encoding/xml/#Decoder.Decode"><code>Decode</code></a> method. An
<a href="/pkg/encoding/xml/#Encoder"><code>Encoder</code></a> type was also introduced.
</p>

<p>
The functions <a href="/pkg/encoding/xml/#Marshal"><code>Marshal</code></a>
and <a href="/pkg/encoding/xml/#Unmarshal"><code>Unmarshal</code></a>
work with <code>[]byte</code> values now. To work with streams,
use the new <a href="/pkg/encoding/xml/#Encoder"><code>Encoder</code></a>
and <a href="/pkg/encoding/xml/#Decoder"><code>Decoder</code></a> types.
</p>

<p>
When marshaling or unmarshaling values, the format of supported flags in
field tags has changed to be closer to the
<a href="/pkg/encoding/json"><code>json</code></a> package
(<code>`xml:"name,flag"`</code>). The matching done between field tags, field
names, and the XML attribute and element names is now case-sensitive.
The <code>XMLName</code> field tag, if present, must also match the name
of the XML element being marshaled.
</p>

<p>
<em>Updating</em>:
Running <code>go</code> <code>fix</code> will update most uses of the package except for some calls to
<code>Unmarshal</code>. Special care must be taken with field tags,
since the fix tool will not update them and if not fixed by hand they will
misbehave silently in some cases. For example, the old
<code>"attr"</code> is now written <code>",attr"</code> while plain
<code>"attr"</code> remains valid but with a different meaning.
</p>

<h3 id="expvar">The expvar package</h3>

<p>
In Go 1, the <code>RemoveAll</code> function has been removed.
The <code>Iter</code> function and Iter method on <code>*Map</code> have
been replaced by
<a href="/pkg/expvar/#Do"><code>Do</code></a>
and
<a href="/pkg/expvar/#Map.Do"><code>(*Map).Do</code></a>.
</p>

<p>
<em>Updating</em>:
Most code using <code>expvar</code> will not need changing. The rare code that used
<code>Iter</code> can be updated to pass a closure to <code>Do</code> to achieve the same effect.
</p>

<h3 id="flag">The flag package</h3>

<p>
In Go 1, the interface <a href="/pkg/flag/#Value"><code>flag.Value</code></a> has changed slightly.
The <code>Set</code> method now returns an <code>error</code> instead of
a <code>bool</code> to indicate success or failure.
</p>

<p>
There is also a new kind of flag, <code>Duration</code>, to support argument
values specifying time intervals.
Values for such flags must be given units, just as <code>time.Duration</code>
formats them: <code>10s</code>, <code>1h30m</code>, etc.
</p>

<pre><!--{{code "/doc/progs/go1.go" `/timeout/`}}
-->var timeout = flag.Duration(&#34;timeout&#34;, 30*time.Second, &#34;how long to wait for completion&#34;)</pre>

<p>
<em>Updating</em>:
Programs that implement their own flags will need minor manual fixes to update their
<code>Set</code> methods.
The <code>Duration</code> flag is new and affects no existing code.
</p>


<h3 id="go">The go/* packages</h3>

<p>
Several packages under <code>go</code> have slightly revised APIs.
</p>

<p>
A concrete <code>Mode</code> type was introduced for configuration mode flags
in the packages
<a href="/pkg/go/scanner/"><code>go/scanner</code></a>,
<a href="/pkg/go/parser/"><code>go/parser</code></a>,
<a href="/pkg/go/printer/"><code>go/printer</code></a>, and
<a href="/pkg/go/doc/"><code>go/doc</code></a>.
</p>

<p>
The modes <code>AllowIllegalChars</code> and <code>InsertSemis</code> have been removed
from the <a href="/pkg/go/scanner/"><code>go/scanner</code></a> package. They were mostly
useful for scanning text other then Go source files. Instead, the
<a href="/pkg/text/scanner/"><code>text/scanner</code></a> package should be used
for that purpose.
</p>

<p>
The <a href="/pkg/go/scanner/#ErrorHandler"><code>ErrorHandler</code></a> provided
to the scanner's <a href="/pkg/go/scanner/#Scanner.Init"><code>Init</code></a> method is
now simply a function rather than an interface. The <code>ErrorVector</code> type has
been removed in favor of the (existing) <a href="/pkg/go/scanner/#ErrorList"><code>ErrorList</code></a>
type, and the <code>ErrorVector</code> methods have been migrated. Instead of embedding
an <code>ErrorVector</code> in a client of the scanner, now a client should maintain
an <code>ErrorList</code>.
</p>

<p>
The set of parse functions provided by the <a href="/pkg/go/parser/"><code>go/parser</code></a>
package has been reduced to the primary parse function
<a href="/pkg/go/parser/#ParseFile"><code>ParseFile</code></a>, and a couple of
convenience functions <a href="/pkg/go/parser/#ParseDir"><code>ParseDir</code></a>
and <a href="/pkg/go/parser/#ParseExpr"><code>ParseExpr</code></a>.
</p>

<p>
The <a href="/pkg/go/printer/"><code>go/printer</code></a> package supports an additional
configuration mode <a href="/pkg/go/printer/#Mode"><code>SourcePos</code></a>;
if set, the printer will emit <code>//line</code> comments such that the generated
output contains the original source code position information. The new type
<a href="/pkg/go/printer/#CommentedNode"><code>CommentedNode</code></a> can be
used to provide comments associated with an arbitrary
<a href="/pkg/go/ast/#Node"><code>ast.Node</code></a> (until now only
<a href="/pkg/go/ast/#File"><code>ast.File</code></a> carried comment information).
</p>

<p>
The type names of the <a href="/pkg/go/doc/"><code>go/doc</code></a> package have been
streamlined by removing the <code>Doc</code> suffix: <code>PackageDoc</code>
is now <code>Package</code>, <code>ValueDoc</code> is <code>Value</code>, etc.
Also, all types now consistently have a <code>Name</code> field (or <code>Names</code>,
in the case of type <code>Value</code>) and <code>Type.Factories</code> has become
<code>Type.Funcs</code>.
Instead of calling <code>doc.NewPackageDoc(pkg, importpath)</code>,
documentation for a package is created with:
</p>

<pre>
    doc.New(pkg, importpath, mode)
</pre>

<p>
where the new <code>mode</code> parameter specifies the operation mode:
if set to <a href="/pkg/go/doc/#AllDecls"><code>AllDecls</code></a>, all declarations
(not just exported ones) are considered.
The function <code>NewFileDoc</code> was removed, and the function
<code>CommentText</code> has become the method
<a href="/pkg/go/ast/#Text"><code>Text</code></a> of
<a href="/pkg/go/ast/#CommentGroup"><code>ast.CommentGroup</code></a>.
</p>

<p>
In package <a href="/pkg/go/token/"><code>go/token</code></a>, the
<a href="/pkg/go/token/#FileSet"><code>token.FileSet</code></a> method <code>Files</code>
(which originally returned a channel of <code>*token.File</code>s) has been replaced
with the iterator <a href="/pkg/go/token/#FileSet.Iterate"><code>Iterate</code></a> that
accepts a function argument instead.
</p>

<p>
In package <a href="/pkg/go/build/"><code>go/build</code></a>, the API
has been nearly completely replaced.
The package still computes Go package information
but it does not run the build: the <code>Cmd</code> and <code>Script</code>
types are gone.
(To build code, use the new
<a href="/cmd/go/"><code>go</code></a> command instead.)
The <code>DirInfo</code> type is now named
<a href="/pkg/go/build/#Package"><code>Package</code></a>.
<code>FindTree</code> and <code>ScanDir</code> are replaced by
<a href="/pkg/go/build/#Import"><code>Import</code></a>
and
<a href="/pkg/go/build/#ImportDir"><code>ImportDir</code></a>.
</p>

<p>
<em>Updating</em>:
Code that uses packages in <code>go</code> will have to be updated by hand; the
compiler will reject incorrect uses. Templates used in conjunction with any of the
<code>go/doc</code> types may need manual fixes; the renamed fields will lead
to run-time errors.
</p>

<h3 id="hash">The hash package</h3>

<p>
In Go 1, the definition of <a href="/pkg/hash/#Hash"><code>hash.Hash</code></a> includes
a new method, <code>BlockSize</code>.  This new method is used primarily in the
cryptographic libraries.
</p>

<p>
The <code>Sum</code> method of the
<a href="/pkg/hash/#Hash"><code>hash.Hash</code></a> interface now takes a
<code>[]byte</code> argument, to which the hash value will be appended.
The previous behavior can be recreated by adding a <code>nil</code> argument to the call.
</p>

<p>
<em>Updating</em>:
Existing implementations of <code>hash.Hash</code> will need to add a
<code>BlockSize</code> method.  Hashes that process the input one byte at
a time can implement <code>BlockSize</code> to return 1.
Running <code>go</code> <code>fix</code> will update calls to the <code>Sum</code> methods of the various
implementations of <code>hash.Hash</code>.
</p>

<p>
<em>Updating</em>:
Since the package's functionality is new, no updating is necessary.
</p>

<h3 id="http">The http package</h3>

<p>
In Go 1 the <a href="/pkg/net/http/"><code>http</code></a> package is refactored,
putting some of the utilities into a
<a href="/pkg/net/http/httputil/"><code>httputil</code></a> subdirectory.
These pieces are only rarely needed by HTTP clients.
The affected items are:
</p>

<ul>
<li>ClientConn</li>
<li>DumpRequest</li>
<li>DumpRequestOut</li>
<li>DumpResponse</li>
<li>NewChunkedReader</li>
<li>NewChunkedWriter</li>
<li>NewClientConn</li>
<li>NewProxyClientConn</li>
<li>NewServerConn</li>
<li>NewSingleHostReverseProxy</li>
<li>ReverseProxy</li>
<li>ServerConn</li>
</ul>

<p>
The <code>Request.RawURL</code> field has been removed; it was a
historical artifact.
</p>

<p>
The <code>Handle</code> and <code>HandleFunc</code>
functions, and the similarly-named methods of <code>ServeMux</code>,
now panic if an attempt is made to register the same pattern twice.
</p>

<p>
<em>Updating</em>:
Running <code>go</code> <code>fix</code> will update the few programs that are affected except for
uses of <code>RawURL</code>, which must be fixed by hand.
</p>

<h3 id="image">The image package</h3>

<p>
The <a href="/pkg/image/"><code>image</code></a> package has had a number of
minor changes, rearrangements and renamings.
</p>

<p>
Most of the color handling code has been moved into its own package,
<a href="/pkg/image/color/"><code>image/color</code></a>.
For the elements that moved, a symmetry arises; for instance,
each pixel of an
<a href="/pkg/image/#RGBA"><code>image.RGBA</code></a>
is a
<a href="/pkg/image/color/#RGBA"><code>color.RGBA</code></a>.
</p>

<p>
The old <code>image/ycbcr</code> package has been folded, with some
renamings, into the
<a href="/pkg/image/"><code>image</code></a>
and
<a href="/pkg/image/color/"><code>image/color</code></a>
packages.
</p>

<p>
The old <code>image.ColorImage</code> type is still in the <code>image</code>
package but has been renamed
<a href="/pkg/image/#Uniform"><code>image.Uniform</code></a>,
while <code>image.Tiled</code> has been removed.
</p>

<p>
This table lists the renamings.
</p>

<table class="codetable" frame="border" summary="image renames">
<colgroup align="left" width="50%"></colgroup>
<colgroup align="left" width="50%"></colgroup>
<tr>
<th align="left">Old</th>
<th align="left">New</th>
</tr>
<tr>
<td colspan="2"><hr></td>
</tr>
<tr><td>image.Color</td> <td>color.Color</td></tr>
<tr><td>image.ColorModel</td> <td>color.Model</td></tr>
<tr><td>image.ColorModelFunc</td> <td>color.ModelFunc</td></tr>
<tr><td>image.PalettedColorModel</td> <td>color.Palette</td></tr>
<tr>
<td colspan="2"><hr></td>
</tr>
<tr><td>image.RGBAColor</td> <td>color.RGBA</td></tr>
<tr><td>image.RGBA64Color</td> <td>color.RGBA64</td></tr>
<tr><td>image.NRGBAColor</td> <td>color.NRGBA</td></tr>
<tr><td>image.NRGBA64Color</td> <td>color.NRGBA64</td></tr>
<tr><td>image.AlphaColor</td> <td>color.Alpha</td></tr>
<tr><td>image.Alpha16Color</td> <td>color.Alpha16</td></tr>
<tr><td>image.GrayColor</td> <td>color.Gray</td></tr>
<tr><td>image.Gray16Color</td> <td>color.Gray16</td></tr>
<tr>
<td colspan="2"><hr></td>
</tr>
<tr><td>image.RGBAColorModel</td> <td>color.RGBAModel</td></tr>
<tr><td>image.RGBA64ColorModel</td> <td>color.RGBA64Model</td></tr>
<tr><td>image.NRGBAColorModel</td> <td>color.NRGBAModel</td></tr>
<tr><td>image.NRGBA64ColorModel</td> <td>color.NRGBA64Model</td></tr>
<tr><td>image.AlphaColorModel</td> <td>color.AlphaModel</td></tr>
<tr><td>image.Alpha16ColorModel</td> <td>color.Alpha16Model</td></tr>
<tr><td>image.GrayColorModel</td> <td>color.GrayModel</td></tr>
<tr><td>image.Gray16ColorModel</td> <td>color.Gray16Model</td></tr>
<tr>
<td colspan="2"><hr></td>
</tr>
<tr><td>ycbcr.RGBToYCbCr</td> <td>color.RGBToYCbCr</td></tr>
<tr><td>ycbcr.YCbCrToRGB</td> <td>color.YCbCrToRGB</td></tr>
<tr><td>ycbcr.YCbCrColorModel</td> <td>color.YCbCrModel</td></tr>
<tr><td>ycbcr.YCbCrColor</td> <td>color.YCbCr</td></tr>
<tr><td>ycbcr.YCbCr</td> <td>image.YCbCr</td></tr>
<tr>
<td colspan="2"><hr></td>
</tr>
<tr><td>ycbcr.SubsampleRatio444</td> <td>image.YCbCrSubsampleRatio444</td></tr>
<tr><td>ycbcr.SubsampleRatio422</td> <td>image.YCbCrSubsampleRatio422</td></tr>
<tr><td>ycbcr.SubsampleRatio420</td> <td>image.YCbCrSubsampleRatio420</td></tr>
<tr>
<td colspan="2"><hr></td>
</tr>
<tr><td>image.ColorImage</td> <td>image.Uniform</td></tr>
</table>

<p>
The image package's <code>New</code> functions
(<a href="/pkg/image/#NewRGBA"><code>NewRGBA</code></a>,
<a href="/pkg/image/#NewRGBA64"><code>NewRGBA64</code></a>, etc.)
take an <a href="/pkg/image/#Rectangle"><code>image.Rectangle</code></a> as an argument
instead of four integers.
</p>

<p>
Finally, there are new predefined <code>color.Color</code> variables
<a href="/pkg/image/color/#Black"><code>color.Black</code></a>,
<a href="/pkg/image/color/#White"><code>color.White</code></a>,
<a href="/pkg/image/color/#Opaque"><code>color.Opaque</code></a>
and
<a href="/pkg/image/color/#Transparent"><code>color.Transparent</code></a>.
</p>

<p>
<em>Updating</em>:
Running <code>go</code> <code>fix</code> will update almost all code affected by the change.
</p>

<h3 id="log_syslog">The log/syslog package</h3>

<p>
In Go 1, the <a href="/pkg/log/syslog/#NewLogger"><code>syslog.NewLogger</code></a>
function returns an error as well as a <code>log.Logger</code>.
</p>

<p>
<em>Updating</em>:
What little code is affected will be caught by the compiler and must be updated by hand.
</p>

<h3 id="mime">The mime package</h3>

<p>
In Go 1, the <a href="/pkg/mime/#FormatMediaType"><code>FormatMediaType</code></a> function
of the <code>mime</code> package has  been simplified to make it
consistent with
<a href="/pkg/mime/#ParseMediaType"><code>ParseMediaType</code></a>.
It now takes <code>"text/html"</code> rather than <code>"text"</code> and <code>"html"</code>.
</p>

<p>
<em>Updating</em>:
What little code is affected will be caught by the compiler and must be updated by hand.
</p>

<h3 id="net">The net package</h3>

<p>
In Go 1, the various <code>SetTimeout</code>,
<code>SetReadTimeout</code>, and <code>SetWriteTimeout</code> methods
have been replaced with
<a href="/pkg/net/#IPConn.SetDeadline"><code>SetDeadline</code></a>,
<a href="/pkg/net/#IPConn.SetReadDeadline"><code>SetReadDeadline</code></a>, and
<a href="/pkg/net/#IPConn.SetWriteDeadline"><code>SetWriteDeadline</code></a>,
respectively.  Rather than taking a timeout value in nanoseconds that
apply to any activity on the connection, the new methods set an
absolute deadline (as a <code>time.Time</code> value) after which
reads and writes will time out and no longer block.
</p>

<p>
There are also new functions
<a href="/pkg/net/#DialTimeout"><code>net.DialTimeout</code></a>
to simplify timing out dialing a network address and
<a href="/pkg/net/#ListenMulticastUDP"><code>net.ListenMulticastUDP</code></a>
to allow multicast UDP to listen concurrently across multiple listeners.
The <code>net.ListenMulticastUDP</code> function replaces the old
<code>JoinGroup</code> and <code>LeaveGroup</code> methods.
</p>

<p>
<em>Updating</em>:
Code that uses the old methods will fail to compile and must be updated by hand.
The semantic change makes it difficult for the fix tool to update automatically.
</p>

<h3 id="os">The os package</h3>

<p>
The <code>Time</code> function has been removed; callers should use
the <a href="/pkg/time/#Time"><code>Time</code></a> type from the
<code>time</code> package.
</p>

<p>
The <code>Exec</code> function has been removed; callers should use
<code>Exec</code> from the <code>syscall</code> package, where available.
</p>

<p>
The <code>ShellExpand</code> function has been renamed to <a
href="/pkg/os/#ExpandEnv"><code>ExpandEnv</code></a>.
</p>

<p>
The <a href="/pkg/os/#NewFile"><code>NewFile</code></a> function
now takes a <code>uintptr</code> fd, instead of an <code>int</code>.
The <a href="/pkg/os/#File.Fd"><code>Fd</code></a> method on files now
also returns a <code>uintptr</code>.
</p>

<p>
There are no longer error constants such as <code>EINVAL</code>
in the <code>os</code> package, since the set of values varied with
the underlying operating system. There are new portable functions like
<a href="/pkg/os/#IsPermission"><code>IsPermission</code></a>
to test common error properties, plus a few new error values
with more Go-like names, such as
<a href="/pkg/os/#ErrPermission"><code>ErrPermission</code></a>
and
<a href="/pkg/os/#ErrNoEnv"><code>ErrNoEnv</code></a>.
</p>

<p>
The <code>Getenverror</code> function has been removed. To distinguish
between a non-existent environment variable and an empty string,
use <a href="/pkg/os/#Environ"><code>os.Environ</code></a> or
<a href="/pkg/syscall/#Getenv"><code>syscall.Getenv</code></a>.
</p>


<p>
The <a href="/pkg/os/#Process.Wait"><code>Process.Wait</code></a> method has
dropped its option argument and the associated constants are gone
from the package.
Also, the function <code>Wait</code> is gone; only the method of
the <code>Process</code> type persists.
</p>

<p>
The <code>Waitmsg</code> type returned by
<a href="/pkg/os/#Process.Wait"><code>Process.Wait</code></a>
has been replaced with a more portable
<a href="/pkg/os/#ProcessState"><code>ProcessState</code></a>
type with accessor methods to recover information about the
process.
Because of changes to <code>Wait</code>, the <code>ProcessState</code>
value always describes an exited process.
Portability concerns simplified the interface in other ways, but the values returned by the
<a href="/pkg/os/#ProcessState.Sys"><code>ProcessState.Sys</code></a> and
<a href="/pkg/os/#ProcessState.SysUsage"><code>ProcessState.SysUsage</code></a>
methods can be type-asserted to underlying system-specific data structures such as
<a href="/pkg/syscall/#WaitStatus"><code>syscall.WaitStatus</code></a> and
<a href="/pkg/syscall/#Rusage"><code>syscall.Rusage</code></a> on Unix.
</p>

<p>
<em>Updating</em>:
Running <code>go</code> <code>fix</code> will drop a zero argument to <code>Process.Wait</code>.
All other changes will be caught by the compiler and must be updated by hand.
</p>

<h4 id="os_fileinfo">The os.FileInfo type</h4>

<p>
Go 1 redefines the <a href="/pkg/os/#FileInfo"><code>os.FileInfo</code></a> type,
changing it from a struct to an interface:
</p>

<pre>
    type FileInfo interface {
        Name() string       // base name of the file
        Size() int64        // length in bytes
        Mode() FileMode     // file mode bits
        ModTime() time.Time // modification time
        IsDir() bool        // abbreviation for Mode().IsDir()
        Sys() interface{}   // underlying data source (can return nil)
    }
</pre>

<p>
The file mode information has been moved into a subtype called
<a href="/pkg/os/#FileMode"><code>os.FileMode</code></a>,
a simple integer type with <code>IsDir</code>, <code>Perm</code>, and <code>String</code>
methods.
</p>

<p>
The system-specific details of file modes and properties such as (on Unix)
i-number have been removed from <code>FileInfo</code> altogether.
Instead, each operating system's <code>os</code> package provides an
implementation of the <code>FileInfo</code> interface, which
has a <code>Sys</code> method that returns the
system-specific representation of file metadata.
For instance, to discover the i-number of a file on a Unix system, unpack
the <code>FileInfo</code> like this:
</p>

<pre>
    fi, err := os.Stat("hello.go")
    if err != nil {
        log.Fatal(err)
    }
    // Check that it's a Unix file.
    unixStat, ok := fi.Sys().(*syscall.Stat_t)
    if !ok {
        log.Fatal("hello.go: not a Unix file")
    }
    fmt.Printf("file i-number: %d\n", unixStat.Ino)
</pre>

<p>
Assuming (which is unwise) that <code>"hello.go"</code> is a Unix file,
the i-number expression could be contracted to
</p>

<pre>
    fi.Sys().(*syscall.Stat_t).Ino
</pre>

<p>
The vast majority of uses of <code>FileInfo</code> need only the methods
of the standard interface.
</p>

<p>
The <code>os</code> package no longer contains wrappers for the POSIX errors
such as <code>ENOENT</code>.
For the few programs that need to verify particular error conditions, there are
now the boolean functions
<a href="/pkg/os/#IsExist"><code>IsExist</code></a>,
<a href="/pkg/os/#IsNotExist"><code>IsNotExist</code></a>
and
<a href="/pkg/os/#IsPermission"><code>IsPermission</code></a>.
</p>

<pre><!--{{code "/doc/progs/go1.go" `/os\.Open/` `/}/`}}
-->    f, err := os.OpenFile(name, os.O_RDWR|os.O_CREATE|os.O_EXCL, 0600)
    if os.IsExist(err) {
        log.Printf(&#34;%s already exists&#34;, name)
    }</pre>

<p>
<em>Updating</em>:
Running <code>go</code> <code>fix</code> will update code that uses the old equivalent of the current <code>os.FileInfo</code>
and <code>os.FileMode</code> API.
Code that needs system-specific file details will need to be updated by hand.
Code that uses the old POSIX error values from the <code>os</code> package
will fail to compile and will also need to be updated by hand.
</p>

<h3 id="os_signal">The os/signal package</h3>

<p>
The <code>os/signal</code> package in Go 1 replaces the
<code>Incoming</code> function, which returned a channel
that received all incoming signals,
with the selective <code>Notify</code> function, which asks
for delivery of specific signals on an existing channel.
</p>

<p>
<em>Updating</em>:
Code must be updated by hand.
A literal translation of
</p>
<pre>
c := signal.Incoming()
</pre>
<p>
is
</p>
<pre>
c := make(chan os.Signal)
signal.Notify(c) // ask for all signals
</pre>
<p>
but most code should list the specific signals it wants to handle instead:
</p>
<pre>
c := make(chan os.Signal)
signal.Notify(c, syscall.SIGHUP, syscall.SIGQUIT)
</pre>

<h3 id="path_filepath">The path/filepath package</h3>

<p>
In Go 1, the <a href="/pkg/path/filepath/#Walk"><code>Walk</code></a> function of the
<code>path/filepath</code> package
has been changed to take a function value of type
<a href="/pkg/path/filepath/#WalkFunc"><code>WalkFunc</code></a>
instead of a <code>Visitor</code> interface value.
<code>WalkFunc</code> unifies the handling of both files and directories.
</p>

<pre>
    type WalkFunc func(path string, info os.FileInfo, err error) error
</pre>

<p>
The <code>WalkFunc</code> function will be called even for files or directories that could not be opened;
in such cases the error argument will describe the failure.
If a directory's contents are to be skipped,
the function should return the value <a href="/pkg/path/filepath/#variables"><code>filepath.SkipDir</code></a>
</p>

<pre><!--{{code "/doc/progs/go1.go" `/STARTWALK/` `/ENDWALK/`}}
-->    markFn := func(path string, info os.FileInfo, err error) error {
        if path == &#34;pictures&#34; { <span class="comment">// Will skip walking of directory pictures and its contents.</span>
            return filepath.SkipDir
        }
        if err != nil {
            return err
        }
        log.Println(path)
        return nil
    }
    err := filepath.Walk(&#34;.&#34;, markFn)
    if err != nil {
        log.Fatal(err)
    }</pre>

<p>
<em>Updating</em>:
The change simplifies most code but has subtle consequences, so affected programs
will need to be updated by hand.
The compiler will catch code using the old interface.
</p>

<h3 id="regexp">The regexp package</h3>

<p>
The <a href="/pkg/regexp/"><code>regexp</code></a> package has been rewritten.
It has the same interface but the specification of the regular expressions
it supports has changed from the old "egrep" form to that of
<a href="http://code.google.com/p/re2/">RE2</a>.
</p>

<p>
<em>Updating</em>:
Code that uses the package should have its regular expressions checked by hand.
</p>

<h3 id="runtime">The runtime package</h3>

<p>
In Go 1, much of the API exported by package
<code>runtime</code> has been removed in favor of
functionality provided by other packages.
Code using the <code>runtime.Type</code> interface
or its specific concrete type implementations should
now use package <a href="/pkg/reflect/"><code>reflect</code></a>.
Code using <code>runtime.Semacquire</code> or <code>runtime.Semrelease</code>
should use channels or the abstractions in package <a href="/pkg/sync/"><code>sync</code></a>.
The <code>runtime.Alloc</code>, <code>runtime.Free</code>,
and <code>runtime.Lookup</code> functions, an unsafe API created for
debugging the memory allocator, have no replacement.
</p>

<p>
Before, <code>runtime.MemStats</code> was a global variable holding
statistics about memory allocation, and calls to <code>runtime.UpdateMemStats</code>
ensured that it was up to date.
In Go 1, <code>runtime.MemStats</code> is a struct type, and code should use
<a href="/pkg/runtime/#ReadMemStats"><code>runtime.ReadMemStats</code></a>
to obtain the current statistics.
</p>

<p>
The package adds a new function,
<a href="/pkg/runtime/#NumCPU"><code>runtime.NumCPU</code></a>, that returns the number of CPUs available
for parallel execution, as reported by the operating system kernel.
Its value can inform the setting of <code>GOMAXPROCS</code>.
The <code>runtime.Cgocalls</code> and <code>runtime.Goroutines</code> functions
have been renamed to <code>runtime.NumCgoCall</code> and <code>runtime.NumGoroutine</code>.
</p>

<p>
<em>Updating</em>:
Running <code>go</code> <code>fix</code> will update code for the function renamings.
Other code will need to be updated by hand.
</p>

<h3 id="strconv">The strconv package</h3>

<p>
In Go 1, the
<a href="/pkg/strconv/"><code>strconv</code></a>
package has been significantly reworked to make it more Go-like and less C-like,
although <code>Atoi</code> lives on (it's similar to
<code>int(ParseInt(x, 10, 0))</code>, as does
<code>Itoa(x)</code> (<code>FormatInt(int64(x), 10)</code>).
There are also new variants of some of the functions that append to byte slices rather than
return strings, to allow control over allocation.
</p>

<p>
This table summarizes the renamings; see the
<a href="/pkg/strconv/">package documentation</a>
for full details.
</p>

<table class="codetable" frame="border" summary="strconv renames">
<colgroup align="left" width="50%"></colgroup>
<colgroup align="left" width="50%"></colgroup>
<tr>
<th align="left">Old call</th>
<th align="left">New call</th>
</tr>
<tr>
<td colspan="2"><hr></td>
</tr>
<tr><td>Atob(x)</td> <td>ParseBool(x)</td></tr>
<tr>
<td colspan="2"><hr></td>
</tr>
<tr><td>Atof32(x)</td> <td>ParseFloat(x, 32)§</td></tr>
<tr><td>Atof64(x)</td> <td>ParseFloat(x, 64)</td></tr>
<tr><td>AtofN(x, n)</td> <td>ParseFloat(x, n)</td></tr>
<tr>
<td colspan="2"><hr></td>
</tr>
<tr><td>Atoi(x)</td> <td>Atoi(x)</td></tr>
<tr><td>Atoi(x)</td> <td>ParseInt(x, 10, 0)§</td></tr>
<tr><td>Atoi64(x)</td> <td>ParseInt(x, 10, 64)</td></tr>
<tr>
<td colspan="2"><hr></td>
</tr>
<tr><td>Atoui(x)</td> <td>ParseUint(x, 10, 0)§</td></tr>
<tr><td>Atoui64(x)</td> <td>ParseUint(x, 10, 64)</td></tr>
<tr>
<td colspan="2"><hr></td>
</tr>
<tr><td>Btoi64(x, b)</td> <td>ParseInt(x, b, 64)</td></tr>
<tr><td>Btoui64(x, b)</td> <td>ParseUint(x, b, 64)</td></tr>
<tr>
<td colspan="2"><hr></td>
</tr>
<tr><td>Btoa(x)</td> <td>FormatBool(x)</td></tr>
<tr>
<td colspan="2"><hr></td>
</tr>
<tr><td>Ftoa32(x, f, p)</td> <td>FormatFloat(float64(x), f, p, 32)</td></tr>
<tr><td>Ftoa64(x, f, p)</td> <td>FormatFloat(x, f, p, 64)</td></tr>
<tr><td>FtoaN(x, f, p, n)</td> <td>FormatFloat(x, f, p, n)</td></tr>
<tr>
<td colspan="2"><hr></td>
</tr>
<tr><td>Itoa(x)</td> <td>Itoa(x)</td></tr>
<tr><td>Itoa(x)</td> <td>FormatInt(int64(x), 10)</td></tr>
<tr><td>Itoa64(x)</td> <td>FormatInt(x, 10)</td></tr>
<tr>
<td colspan="2"><hr></td>
</tr>
<tr><td>Itob(x, b)</td> <td>FormatInt(int64(x), b)</td></tr>
<tr><td>Itob64(x, b)</td> <td>FormatInt(x, b)</td></tr>
<tr>
<td colspan="2"><hr></td>
</tr>
<tr><td>Uitoa(x)</td> <td>FormatUint(uint64(x), 10)</td></tr>
<tr><td>Uitoa64(x)</td> <td>FormatUint(x, 10)</td></tr>
<tr>
<td colspan="2"><hr></td>
</tr>
<tr><td>Uitob(x, b)</td> <td>FormatUint(uint64(x), b)</td></tr>
<tr><td>Uitob64(x, b)</td> <td>FormatUint(x, b)</td></tr>
</table>
		
<p>
<em>Updating</em>:
Running <code>go</code> <code>fix</code> will update almost all code affected by the change.
<br>
§ <code>Atoi</code> persists but <code>Atoui</code> and <code>Atof32</code> do not, so
they may require
a cast that must be added by hand; the <code>go</code> <code>fix</code> tool will warn about it.
</p>


<h3 id="templates">The template packages</h3>

<p>
The <code>template</code> and <code>exp/template/html</code> packages have moved to 
<a href="/pkg/text/template/"><code>text/template</code></a> and
<a href="/pkg/html/template/"><code>html/template</code></a>.
More significant, the interface to these packages has been simplified.
The template language is the same, but the concept of "template set" is gone
and the functions and methods of the packages have changed accordingly,
often by elimination.
</p>

<p>
Instead of sets, a <code>Template</code> object
may contain multiple named template definitions,
in effect constructing
name spaces for template invocation.
A template can invoke any other template associated with it, but only those
templates associated with it.
The simplest way to associate templates is to parse them together, something
made easier with the new structure of the packages.
</p>

<p>
<em>Updating</em>:
The imports will be updated by fix tool.
Single-template uses will be otherwise be largely unaffected.
Code that uses multiple templates in concert will need to be updated by hand.
The <a href="/pkg/text/template/#examples">examples</a> in
the documentation for <code>text/template</code> can provide guidance.
</p>

<h3 id="testing">The testing package</h3>

<p>
The testing package has a type, <code>B</code>, passed as an argument to benchmark functions.
In Go 1, <code>B</code> has new methods, analogous to those of <code>T</code>, enabling
logging and failure reporting.
</p>

<pre><!--{{code "/doc/progs/go1.go" `/func.*Benchmark/` `/^}/`}}
-->func BenchmarkSprintf(b *testing.B) {
    <span class="comment">// Verify correctness before running benchmark.</span>
    b.StopTimer()
    got := fmt.Sprintf(&#34;%x&#34;, 23)
    const expect = &#34;17&#34;
    if expect != got {
        b.Fatalf(&#34;expected %q; got %q&#34;, expect, got)
    }
    b.StartTimer()
    for i := 0; i &lt; b.N; i++ {
        fmt.Sprintf(&#34;%x&#34;, 23)
    }
}</pre>

<p>
<em>Updating</em>:
Existing code is unaffected, although benchmarks that use <code>println</code>
or <code>panic</code> should be updated to use the new methods.
</p>

<h3 id="testing_script">The testing/script package</h3>

<p>
The testing/script package has been deleted. It was a dreg.
</p>

<p>
<em>Updating</em>:
No code is likely to be affected.
</p>

<h3 id="unsafe">The unsafe package</h3>

<p>
In Go 1, the functions
<code>unsafe.Typeof</code>, <code>unsafe.Reflect</code>,
<code>unsafe.Unreflect</code>, <code>unsafe.New</code>, and
<code>unsafe.NewArray</code> have been removed;
they duplicated safer functionality provided by
package <a href="/pkg/reflect/"><code>reflect</code></a>.
</p>

<p>
<em>Updating</em>:
Code using these functions must be rewritten to use
package <a href="/pkg/reflect/"><code>reflect</code></a>.
The changes to <a href="http://code.google.com/p/go/source/detail?r=2646dc956207">encoding/gob</a> and the <a href="http://code.google.com/p/goprotobuf/source/detail?r=5340ad310031">protocol buffer library</a>
may be helpful as examples.
</p>

<h3 id="url">The url package</h3>

<p>
In Go 1 several fields from the <a href="/pkg/net/url/#URL"><code>url.URL</code></a> type
were removed or replaced.
</p>

<p>
The <a href="/pkg/net/url/#URL.String"><code>String</code></a> method now
predictably rebuilds an encoded URL string using all of <code>URL</code>'s
fields as necessary. The resulting string will also no longer have
passwords escaped.
</p>

<p>
The <code>Raw</code> field has been removed. In most cases the <code>String</code>
method may be used in its place.
</p>

<p>
The old <code>RawUserinfo</code> field is replaced by the <code>User</code>
field, of type <a href="/pkg/net/url/#Userinfo"><code>*net.Userinfo</code></a>.
Values of this type may be created using the new <a href="/pkg/net/url/#User"><code>net.User</code></a>
and <a href="/pkg/net/url/#UserPassword"><code>net.UserPassword</code></a>
functions. The <code>EscapeUserinfo</code> and <code>UnescapeUserinfo</code>
functions are also gone.
</p>

<p>
The <code>RawAuthority</code> field has been removed. The same information is
available in the <code>Host</code> and <code>User</code> fields.
</p>

<p>
The <code>RawPath</code> field and the <code>EncodedPath</code> method have
been removed. The path information in rooted URLs (with a slash following the
schema) is now available only in decoded form in the <code>Path</code> field.
Occasionally, the encoded data may be required to obtain information that
was lost in the decoding process. These cases must be handled by accessing
the data the URL was built from.
</p>

<p>
URLs with non-rooted paths, such as <code>"mailto:dev@golang.org?subject=Hi"</code>,
are also handled differently. The <code>OpaquePath</code> boolean field has been
removed and a new <code>Opaque</code> string field introduced to hold the encoded
path for such URLs. In Go 1, the cited URL parses as:
</p>

<pre>
    URL{
        Scheme: "mailto",
        Opaque: "dev@golang.org",
        RawQuery: "subject=Hi",
    }
</pre>

<p>
A new <a href="/pkg/net/url/#URL.RequestURI"><code>RequestURI</code></a> method was
added to <code>URL</code>.
</p>

<p>
The <code>ParseWithReference</code> function has been renamed to <code>ParseWithFragment</code>.
</p>

<p>
<em>Updating</em>:
Code that uses the old fields will fail to compile and must be updated by hand.
The semantic changes make it difficult for the fix tool to update automatically.
</p>

<h2 id="cmd_go">The go command</h2>

<p>
Go 1 introduces the <a href="/cmd/go/">go command</a>, a tool for fetching,
building, and installing Go packages and commands. The <code>go</code> command
does away with makefiles, instead using Go source code to find dependencies and
determine build conditions. Most existing Go programs will no longer require
makefiles to be built.
</p>

<p>
See <a href="/doc/code.html">How to Write Go Code</a> for a primer on the
<code>go</code> command and the <a href="/cmd/go/">go command documentation</a>
for the full details.
</p>

<p>
<em>Updating</em>:
Projects that depend on the Go project's old makefile-based build
infrastructure (<code>Make.pkg</code>, <code>Make.cmd</code>, and so on) should
switch to using the <code>go</code> command for building Go code and, if
necessary, rewrite their makefiles to perform any auxiliary build tasks.
</p>

<h2 id="cmd_cgo">The cgo command</h2>

<p>
In Go 1, the <a href="/cmd/cgo">cgo command</a>
uses a different <code>_cgo_export.h</code>
file, which is generated for packages containing <code>//export</code> lines.
The <code>_cgo_export.h</code> file now begins with the C preamble comment,
so that exported function definitions can use types defined there.
This has the effect of compiling the preamble multiple times, so a
package using <code>//export</code> must not put function definitions
or variable initializations in the C preamble.
</p>

<h2 id="releases">Packaged releases</h2>

<p>
One of the most significant changes associated with Go 1 is the availability
of prepackaged, downloadable distributions.
They are available for many combinations of architecture and operating system
(including Windows) and the list will grow.
Installation details are described on the
<a href="/doc/install">Getting Started</a> page, while
the distributions themselves are listed on the
<a href="http://code.google.com/p/go/downloads/list">downloads page</a>.


</div>

<div id="footer">
Build version go1.0.1.<br>
Except as <a href="http://code.google.com/policies.html#restrictions">noted</a>,
the content of this page is licensed under the
Creative Commons Attribution 3.0 License,
and code is licensed under a <a href="/LICENSE">BSD license</a>.<br>
<a href="/doc/tos.html">Terms of Service</a> | 
<a href="http://www.google.com/intl/en/privacy/privacy-policy.html">Privacy Policy</a>
</div>

<script type="text/javascript">
(function() {
  var ga = document.createElement("script"); ga.type = "text/javascript"; ga.async = true;
  ga.src = ("https:" == document.location.protocol ? "https://ssl" : "http://www") + ".google-analytics.com/ga.js";
  var s = document.getElementsByTagName("script")[0]; s.parentNode.insertBefore(ga, s);
})();
</script>
</body>
<script type="text/javascript">
  (function() {
    var po = document.createElement('script'); po.type = 'text/javascript'; po.async = true;
    po.src = 'https://apis.google.com/js/plusone.js';
    var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(po, s);
  })();
</script>
</html>
generated by cgit v1.2.3 (git 2.25.1) at 2024-04-28 09:32:58 +0000