http://golang.org/ref/spec#Comparison_operators
Go supports string comparison without any special functions. Does the Go runtime do work behind the scenes to make comparisons of string literals?
As you can see in the following assembly dump, string comparison is delegated to a runtime.eqstring function from the runtime (line 17) after a short circuit check to see if the two operands are the same in-memory string (line 11):
$ cat foo.go
package main
func main() {
a := "hello"
b := "world"
_ = a == b
}
$ go tool 6g -S foo.go
--- prog list "main" ---
0000 (foo.go:3) TEXT main+0(SB),$40-0
0001 (foo.go:3) LOCALS ,$0
0002 (foo.go:4) LEAQ go.string."hello"+0(SB),BX
0003 (foo.go:4) MOVQ (BX),SI
0004 (foo.go:4) MOVQ 8(BX),CX
0005 (foo.go:5) LEAQ go.string."world"+0(SB),BX
0006 (foo.go:5) MOVQ (BX),DX
0007 (foo.go:5) MOVQ 8(BX),AX
0008 (foo.go:6) JMP ,11
0009 (foo.go:6) MOVQ $1,AX
0010 (foo.go:6) JMP ,23
0011 (foo.go:6) CMPQ CX,AX
0012 (foo.go:6) JNE ,22
0013 (foo.go:6) MOVQ SI,(SP)
0014 (foo.go:6) MOVQ CX,8(SP)
0015 (foo.go:6) MOVQ DX,16(SP)
0016 (foo.go:6) MOVQ AX,24(SP)
0017 (foo.go:6) CALL ,runtime.eqstring+0(SB)
0018 (foo.go:6) MOVBQZX 32(SP),BX
0019 (foo.go:6) CMPB BX,$0
0020 (foo.go:6) JEQ ,22
0021 (foo.go:6) JMP ,9
0022 (foo.go:6) MOVQ $0,AX
0023 (foo.go:7) RET ,
--- prog list "init" ---
0024 (foo.go:7) TEXT init+0(SB),$0-0
0025 (foo.go:7) MOVBQZX initdone·+0(SB),AX
0026 (foo.go:7) LOCALS ,$0
0027 (foo.go:7) CMPB AX,$0
0028 (foo.go:7) JEQ ,34
0029 (foo.go:7) CMPB AX,$2
0030 (foo.go:7) JNE ,32
0031 (foo.go:7) RET ,
0032 (foo.go:7) CALL ,runtime.throwinit+0(SB)
0033 (foo.go:7) UNDEF ,
0034 (foo.go:7) MOVB $2,initdone·+0(SB)
0035 (foo.go:7) RET ,
Unless you are working on the compiler or runtime, this shouldn't concern you too much: just use the operators as the spec defines, and expect that the comparison to be O(n) with the length of the string.
runtime/string.goc (go1.3):
func eqstring(s1 String, s2 String) (v bool) {
if(s1.len != s2.len) {
v = false;
return;
}
if(s1.str == s2.str) {
v = true;
return;
}
v = runtime·memeq(s1.str, s2.str, s1.len);
}
int32
runtime·strcmp(byte *s1, byte *s2)
{
uintptr i;
byte c1, c2;
for(i=0;; i++) {
c1 = s1[i];
c2 = s2[i];
if(c1 < c2)
return -1;
if(c1 > c2)
return +1;
if(c1 == 0)
return 0;
}
}
Note: The runtime· separator is a Unicode middle-dot, not a period.