Make ninjaString an interface

There are 8935901 *ninjaString objects generated in an AOSP
aosp_blueline-userdebug build, and 7865180 of those are a literal
string with no ninja variables.
Each of those *ninjaString objects takes a minimum of 48 bytes for
2 slices, plus 8 bytes for the pointer to the ninjaString.  For
the literal string case, one of those slices has a single element,
(costing another 16 bytes for the backing array), and the other
slice is empty, for a total of 72 bytes.

Replace *ninjaString with a ninjaString interface.  This increases
the size of the reference from 8 bytes to 16 bytes, but using
a type alias of a string for the literal string implementation uses
only 16 bytes, saving 40 bytes per literal string or 314 MB.

Test: ninja_strings_test
Change-Id: Ic5fe16ed1f2a244fe6a8ccdf762919634d825cbe

1 files changed, 5 insertions, 5 deletions

diff --git a/live_tracker.go b/live_tracker.go
index 5e13a87..40e1930 100644
--- a/live_tracker.go
+++ b/live_tracker.go
@@ -24,7 +24,7 @@ type liveTracker struct {
 	sync.Mutex
 	config interface{} // Used to evaluate variable, rule, and pool values.
 
-	variables map[Variable]*ninjaString
+	variables map[Variable]ninjaString
 	pools     map[Pool]*poolDef
 	rules     map[Rule]*ruleDef
 }
@@ -32,7 +32,7 @@ type liveTracker struct {
 func newLiveTracker(config interface{}) *liveTracker {
 	return &liveTracker{
 		config:    config,
-		variables: make(map[Variable]*ninjaString),
+		variables: make(map[Variable]ninjaString),
 		pools:     make(map[Pool]*poolDef),
 		rules:     make(map[Rule]*ruleDef),
 	}
@@ -170,7 +170,7 @@ func (l *liveTracker) addVariable(v Variable) error {
 	return nil
 }
 
-func (l *liveTracker) addNinjaStringListDeps(list []*ninjaString) error {
+func (l *liveTracker) addNinjaStringListDeps(list []ninjaString) error {
 	for _, str := range list {
 		err := l.addNinjaStringDeps(str)
 		if err != nil {
@@ -180,8 +180,8 @@ func (l *liveTracker) addNinjaStringListDeps(list []*ninjaString) error {
 	return nil
 }
 
-func (l *liveTracker) addNinjaStringDeps(str *ninjaString) error {
-	for _, v := range str.variables {
+func (l *liveTracker) addNinjaStringDeps(str ninjaString) error {
+	for _, v := range str.Variables() {
 		err := l.addVariable(v)
 		if err != nil {
 			return err