// Copyright 2009 The Go Authors. All rights reserved. // Use of this source code is governed by a BSD-style // license that can be found in the LICENSE file. // Package strings implements simple functions to manipulate strings. package strings import ( "unicode" "unicode/utf8" ) // explode splits s into an array of UTF-8 sequences, one per Unicode character (still strings) up to a maximum of n (n < 0 means no limit). // Invalid UTF-8 sequences become correct encodings of U+FFF8. func explode(s string, n int) []string { if n == 0 { return nil } l := utf8.RuneCountInString(s) if n <= 0 || n > l { n = l } a := make([]string, n) var size int var ch rune i, cur := 0, 0 for ; i+1 < n; i++ { ch, size = utf8.DecodeRuneInString(s[cur:]) if ch == utf8.RuneError { a[i] = string(utf8.RuneError) } else { a[i] = s[cur : cur+size] } cur += size } // add the rest, if there is any if cur < len(s) { a[i] = s[cur:] } return a } // primeRK is the prime base used in Rabin-Karp algorithm. const primeRK = 16777619 // hashstr returns the hash and the appropriate multiplicative // factor for use in Rabin-Karp algorithm. func hashstr(sep string) (uint32, uint32) { hash := uint32(0) for i := 0; i < len(sep); i++ { hash = hash*primeRK + uint32(sep[i]) } var pow, sq uint32 = 1, primeRK for i := len(sep); i > 0; i >>= 1 { if i&1 != 0 { pow *= sq } sq *= sq } return hash, pow } // Count counts the number of non-overlapping instances of sep in s. func Count(s, sep string) int { n := 0 // special cases switch { case len(sep) == 0: return utf8.RuneCountInString(s) + 1 case len(sep) == 1: // special case worth making fast c := sep[0] for i := 0; i < len(s); i++ { if s[i] == c { n++ } } return n case len(sep) > len(s): return 0 case len(sep) == len(s): if sep == s { return 1 } return 0 } hashsep, pow := hashstr(sep) h := uint32(0) for i := 0; i < len(sep); i++ { h = h*primeRK + uint32(s[i]) } lastmatch := 0 if h == hashsep && s[:len(sep)] == sep { n++ lastmatch = len(sep) } for i := len(sep); i < len(s); { h *= primeRK h += uint32(s[i]) h -= pow * uint32(s[i-len(sep)]) i++ if h == hashsep && lastmatch <= i-len(sep) && s[i-len(sep):i] == sep { n++ lastmatch = i } } return n } // Contains returns true if substr is within s. func Contains(s, substr string) bool { return Index(s, substr) >= 0 } // ContainsAny returns true if any Unicode code points in chars are within s. func ContainsAny(s, chars string) bool { return IndexAny(s, chars) >= 0 } // ContainsRune returns true if the Unicode code point r is within s. func ContainsRune(s string, r rune) bool { return IndexRune(s, r) >= 0 } // Index returns the index of the first instance of sep in s, or -1 if sep is not present in s. func Index(s, sep string) int { n := len(sep) switch { case n == 0: return 0 case n == 1: c := sep[0] // special case worth making fast for i := 0; i < len(s); i++ { if s[i] == c { return i } } return -1 case n == len(s): if sep == s { return 0 } return -1 case n > len(s): return -1 } // Hash sep. hashsep, pow := hashstr(sep) var h uint32 for i := 0; i < n; i++ { h = h*primeRK + uint32(s[i]) } if h == hashsep && s[:n] == sep { return 0 } for i := n; i < len(s); { h *= primeRK h += uint32(s[i]) h -= pow * uint32(s[i-n]) i++ if h == hashsep && s[i-n:i] == sep { return i - n } } return -1 } // LastIndex returns the index of the last instance of sep in s, or -1 if sep is not present in s. func LastIndex(s, sep string) int { n := len(sep) if n == 0 { return len(s) } c := sep[0] if n == 1 { // special case worth making fast for i := len(s) - 1; i >= 0; i-- { if s[i] == c { return i } } return -1 } // n > 1 for i := len(s) - n; i >= 0; i-- { if s[i] == c && s[i:i+n] == sep { return i } } return -1 } // IndexRune returns the index of the first instance of the Unicode code point // r, or -1 if rune is not present in s. func IndexRune(s string, r rune) int { switch { case r < 0x80: b := byte(r) for i := 0; i < len(s); i++ { if s[i] == b { return i } } default: for i, c := range s { if c == r { return i } } } return -1 } // IndexAny returns the index of the first instance of any Unicode code point // from chars in s, or -1 if no Unicode code point from chars is present in s. func IndexAny(s, chars string) int { if len(chars) > 0 { for i, c := range s { for _, m := range chars { if c == m { return i } } } } return -1 } // LastIndexAny returns the index of the last instance of any Unicode code // point from chars in s, or -1 if no Unicode code point from chars is // present in s. func LastIndexAny(s, chars string) int { if len(chars) > 0 { for i := len(s); i > 0; { rune, size := utf8.DecodeLastRuneInString(s[0:i]) i -= size for _, m := range chars { if rune == m { return i } } } } return -1 } // Generic split: splits after each instance of sep, // including sepSave bytes of sep in the subarrays. func genSplit(s, sep string, sepSave, n int) []string { if n == 0 { return nil } if sep == "" { return explode(s, n) } if n < 0 { n = Count(s, sep) + 1 } c := sep[0] start := 0 a := make([]string, n) na := 0 for i := 0; i+len(sep) <= len(s) && na+1 < n; i++ { if s[i] == c && (len(sep) == 1 || s[i:i+len(sep)] == sep) { a[na] = s[start : i+sepSave] na++ start = i + len(sep) i += len(sep) - 1 } } a[na] = s[start:] return a[0 : na+1] } // SplitN slices s into substrings separated by sep and returns a slice of // the substrings between those separators. // If sep is empty, SplitN splits after each UTF-8 sequence. // The count determines the number of substrings to return: // n > 0: at most n substrings; the last substring will be the unsplit remainder. // n == 0: the result is nil (zero substrings) // n < 0: all substrings func SplitN(s, sep string, n int) []string { return genSplit(s, sep, 0, n) } // SplitAfterN slices s into substrings after each instance of sep and // returns a slice of those substrings. // If sep is empty, SplitAfterN splits after each UTF-8 sequence. // The count determines the number of substrings to return: // n > 0: at most n substrings; the last substring will be the unsplit remainder. // n == 0: the result is nil (zero substrings) // n < 0: all substrings func SplitAfterN(s, sep string, n int) []string { return genSplit(s, sep, len(sep), n) } // Split slices s into all substrings separated by sep and returns a slice of // the substrings between those separators. // If sep is empty, Split splits after each UTF-8 sequence. // It is equivalent to SplitN with a count of -1. func Split(s, sep string) []string { return genSplit(s, sep, 0, -1) } // SplitAfter slices s into all substrings after each instance of sep and // returns a slice of those substrings. // If sep is empty, SplitAfter splits after each UTF-8 sequence. // It is equivalent to SplitAfterN with a count of -1. func SplitAfter(s, sep string) []string { return genSplit(s, sep, len(sep), -1) } // Fields splits the string s around each instance of one or more consecutive white space // characters, as defined by unicode.IsSpace, returning an array of substrings of s or an // empty list if s contains only white space. func Fields(s string) []string { return FieldsFunc(s, unicode.IsSpace) } // FieldsFunc splits the string s at each run of Unicode code points c satisfying f(c) // and returns an array of slices of s. If all code points in s satisfy f(c) or the // string is empty, an empty slice is returned. func FieldsFunc(s string, f func(rune) bool) []string { // First count the fields. n := 0 inField := false for _, rune := range s { wasInField := inField inField = !f(rune) if inField && !wasInField { n++ } } // Now create them. a := make([]string, n) na := 0 fieldStart := -1 // Set to -1 when looking for start of field. for i, rune := range s { if f(rune) { if fieldStart >= 0 { a[na] = s[fieldStart:i] na++ fieldStart = -1 } } else if fieldStart == -1 { fieldStart = i } } if fieldStart >= 0 { // Last field might end at EOF. a[na] = s[fieldStart:] } return a } // Join concatenates the elements of a to create a single string. The separator string // sep is placed between elements in the resulting string. func Join(a []string, sep string) string { if len(a) == 0 { return "" } if len(a) == 1 { return a[0] } n := len(sep) * (len(a) - 1) for i := 0; i < len(a); i++ { n += len(a[i]) } b := make([]byte, n) bp := copy(b, a[0]) for _, s := range a[1:] { bp += copy(b[bp:], sep) bp += copy(b[bp:], s) } return string(b) } // HasPrefix tests whether the string s begins with prefix. func HasPrefix(s, prefix string) bool { return len(s) >= len(prefix) && s[0:len(prefix)] == prefix } // HasSuffix tests whether the string s ends with suffix. func HasSuffix(s, suffix string) bool { return len(s) >= len(suffix) && s[len(s)-len(suffix):] == suffix } // Map returns a copy of the string s with all its characters modified // according to the mapping function. If mapping returns a negative value, the character is // dropped from the string with no replacement. func Map(mapping func(rune) rune, s string) string { // In the worst case, the string can grow when mapped, making // things unpleasant. But it's so rare we barge in assuming it's // fine. It could also shrink but that falls out naturally. maxbytes := len(s) // length of b nbytes := 0 // number of bytes encoded in b // The output buffer b is initialized on demand, the first // time a character differs. var b []byte for i, c := range s { r := mapping(c) if b == nil { if r == c { continue } b = make([]byte, maxbytes) nbytes = copy(b, s[:i]) } if r >= 0 { wid := 1 if r >= utf8.RuneSelf { wid = utf8.RuneLen(r) } if nbytes+wid > maxbytes { // Grow the buffer. maxbytes = maxbytes*2 + utf8.UTFMax nb := make([]byte, maxbytes) copy(nb, b[0:nbytes]) b = nb } nbytes += utf8.EncodeRune(b[nbytes:maxbytes], r) } } if b == nil { return s } return string(b[0:nbytes]) } // Repeat returns a new string consisting of count copies of the string s. func Repeat(s string, count int) string { b := make([]byte, len(s)*count) bp := 0 for i := 0; i < count; i++ { for j := 0; j < len(s); j++ { b[bp] = s[j] bp++ } } return string(b) } // ToUpper returns a copy of the string s with all Unicode letters mapped to their upper case. func ToUpper(s string) string { return Map(unicode.ToUpper, s) } // ToLower returns a copy of the string s with all Unicode letters mapped to their lower case. func ToLower(s string) string { return Map(unicode.ToLower, s) } // ToTitle returns a copy of the string s with all Unicode letters mapped to their title case. func ToTitle(s string) string { return Map(unicode.ToTitle, s) } // ToUpperSpecial returns a copy of the string s with all Unicode letters mapped to their // upper case, giving priority to the special casing rules. func ToUpperSpecial(_case unicode.SpecialCase, s string) string { return Map(func(r rune) rune { return _case.ToUpper(r) }, s) } // ToLowerSpecial returns a copy of the string s with all Unicode letters mapped to their // lower case, giving priority to the special casing rules. func ToLowerSpecial(_case unicode.SpecialCase, s string) string { return Map(func(r rune) rune { return _case.ToLower(r) }, s) } // ToTitleSpecial returns a copy of the string s with all Unicode letters mapped to their // title case, giving priority to the special casing rules. func ToTitleSpecial(_case unicode.SpecialCase, s string) string { return Map(func(r rune) rune { return _case.ToTitle(r) }, s) } // isSeparator reports whether the rune could mark a word boundary. // TODO: update when package unicode captures more of the properties. func isSeparator(r rune) bool { // ASCII alphanumerics and underscore are not separators if r <= 0x7F { switch { case '0' <= r && r <= '9': return false case 'a' <= r && r <= 'z': return false case 'A' <= r && r <= 'Z': return false case r == '_': return false } return true } // Letters and digits are not separators if unicode.IsLetter(r) || unicode.IsDigit(r) { return false } // Otherwise, all we can do for now is treat spaces as separators. return unicode.IsSpace(r) } // Title returns a copy of the string s with all Unicode letters that begin words // mapped to their title case. // // BUG: The rule Title uses for word boundaries does not handle Unicode punctuation properly. func Title(s string) string { // Use a closure here to remember state. // Hackish but effective. Depends on Map scanning in order and calling // the closure once per rune. prev := ' ' return Map( func(r rune) rune { if isSeparator(prev) { prev = r return unicode.ToTitle(r) } prev = r return r }, s) } // TrimLeftFunc returns a slice of the string s with all leading // Unicode code points c satisfying f(c) removed. func TrimLeftFunc(s string, f func(rune) bool) string { i := indexFunc(s, f, false) if i == -1 { return "" } return s[i:] } // TrimRightFunc returns a slice of the string s with all trailing // Unicode code points c satisfying f(c) removed. func TrimRightFunc(s string, f func(rune) bool) string { i := lastIndexFunc(s, f, false) if i >= 0 && s[i] >= utf8.RuneSelf { _, wid := utf8.DecodeRuneInString(s[i:]) i += wid } else { i++ } return s[0:i] } // TrimFunc returns a slice of the string s with all leading // and trailing Unicode code points c satisfying f(c) removed. func TrimFunc(s string, f func(rune) bool) string { return TrimRightFunc(TrimLeftFunc(s, f), f) } // IndexFunc returns the index into s of the first Unicode // code point satisfying f(c), or -1 if none do. func IndexFunc(s string, f func(rune) bool) int { return indexFunc(s, f, true) } // LastIndexFunc returns the index into s of the last // Unicode code point satisfying f(c), or -1 if none do. func LastIndexFunc(s string, f func(rune) bool) int { return lastIndexFunc(s, f, true) } // indexFunc is the same as IndexFunc except that if // truth==false, the sense of the predicate function is // inverted. func indexFunc(s string, f func(rune) bool, truth bool) int { start := 0 for start < len(s) { wid := 1 r := rune(s[start]) if r >= utf8.RuneSelf { r, wid = utf8.DecodeRuneInString(s[start:]) } if f(r) == truth { return start } start += wid } return -1 } // lastIndexFunc is the same as LastIndexFunc except that if // truth==false, the sense of the predicate function is // inverted. func lastIndexFunc(s string, f func(rune) bool, truth bool) int { for i := len(s); i > 0; { r, size := utf8.DecodeLastRuneInString(s[0:i]) i -= size if f(r) == truth { return i } } return -1 } func makeCutsetFunc(cutset string) func(rune) bool { return func(r rune) bool { return IndexRune(cutset, r) >= 0 } } // Trim returns a slice of the string s with all leading and // trailing Unicode code points contained in cutset removed. func Trim(s string, cutset string) string { if s == "" || cutset == "" { return s } return TrimFunc(s, makeCutsetFunc(cutset)) } // TrimLeft returns a slice of the string s with all leading // Unicode code points contained in cutset removed. func TrimLeft(s string, cutset string) string { if s == "" || cutset == "" { return s } return TrimLeftFunc(s, makeCutsetFunc(cutset)) } // TrimRight returns a slice of the string s, with all trailing // Unicode code points contained in cutset removed. func TrimRight(s string, cutset string) string { if s == "" || cutset == "" { return s } return TrimRightFunc(s, makeCutsetFunc(cutset)) } // TrimSpace returns a slice of the string s, with all leading // and trailing white space removed, as defined by Unicode. func TrimSpace(s string) string { return TrimFunc(s, unicode.IsSpace) } // TrimPrefix returns s without the provided leading prefix string. // If s doesn't start with prefix, s is returned unchanged. func TrimPrefix(s, prefix string) string { if HasPrefix(s, prefix) { return s[len(prefix):] } return s } // TrimSuffix returns s without the provided trailing suffix string. // If s doesn't end with suffix, s is returned unchanged. func TrimSuffix(s, suffix string) string { if HasSuffix(s, suffix) { return s[:len(s)-len(suffix)] } return s } // Replace returns a copy of the string s with the first n // non-overlapping instances of old replaced by new. // If n < 0, there is no limit on the number of replacements. func Replace(s, old, new string, n int) string { if old == new || n == 0 { return s // avoid allocation } // Compute number of replacements. if m := Count(s, old); m == 0 { return s // avoid allocation } else if n < 0 || m < n { n = m } // Apply replacements to buffer. t := make([]byte, len(s)+n*(len(new)-len(old))) w := 0 start := 0 for i := 0; i < n; i++ { j := start if len(old) == 0 { if i > 0 { _, wid := utf8.DecodeRuneInString(s[start:]) j += wid } } else { j += Index(s[start:], old) } w += copy(t[w:], s[start:j]) w += copy(t[w:], new) start = j + len(old) } w += copy(t[w:], s[start:]) return string(t[0:w]) } // EqualFold reports whether s and t, interpreted as UTF-8 strings, // are equal under Unicode case-folding. func EqualFold(s, t string) bool { for s != "" && t != "" { // Extract first rune from each string. var sr, tr rune if s[0] < utf8.RuneSelf { sr, s = rune(s[0]), s[1:] } else { r, size := utf8.DecodeRuneInString(s) sr, s = r, s[size:] } if t[0] < utf8.RuneSelf { tr, t = rune(t[0]), t[1:] } else { r, size := utf8.DecodeRuneInString(t) tr, t = r, t[size:] } // If they match, keep going; if not, return false. // Easy case. if tr == sr { continue } // Make sr < tr to simplify what follows. if tr < sr { tr, sr = sr, tr } // Fast check for ASCII. if tr < utf8.RuneSelf && 'A' <= sr && sr <= 'Z' { // ASCII, and sr is upper case. tr must be lower case. if tr == sr+'a'-'A' { continue } return false } // General case. SimpleFold(x) returns the next equivalent rune > x // or wraps around to smaller values. r := unicode.SimpleFold(sr) for r != sr && r < tr { r = unicode.SimpleFold(r) } if r == tr { continue } return false } // One string is empty. Are both? return s == t }