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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?
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Using Compare() method: You can also compare two strings using the built-in function Compare() provided by the strings package. This function returns an integer value after comparing two strings lexicographically. The return values are: Return 0, if str1 == str2.
The algorithm to compare two strings is simple: Compare the first character of both strings. If the first character from the first string is greater (or less) than the other string's, then the first string is greater (or less) than the second. We're done.
Go supports two styles of string literals, the double-quote style (or interpreted literals) and the back-quote style (or raw string literals). The zero values of string types are blank strings, which can be represented with "" or `` in literal. Strings can be concatenated with + and += operators.
The Go programming language has a small set of known rules for comparing and ordering values. As you saw, while values from all types are comparable using the == (or !=) operator, only a few types can be compared using order operators such as <, >, <=, and >=.
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.
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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.
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