Go 语言字符串常量

Question

Go 中使用的内联字符串和常量字符串之间是否存在差异，或者这是否完全由编译器优化？

具有 100B 次迭代的示例基准代码:

package main

import "fmt"
import "time"
import "log"

func main() {
    // String
    start := time.Now()
    for i := 0; i < 100000000; i++ {
        x := "My String"
        if i % 1000000 == 0{
            fmt.Printf(x)
        }
    }
    elapsed := time.Since(start)
    log.Printf("\nTook %s", elapsed)

    // Constant
    start2 := time.Now()
    const MY_STRING = "My String 2"
    for i := 0; i < 100000000; i++ {
        x := MY_STRING
        if i % 1000000 == 0 {
            fmt.Printf(x)
        }
    }

    elapsed2 := time.Since(start2)
    log.Printf("\nTook %s", elapsed2)

    // Proof that the timer does work :)
    start3 := time.Now()
    time.Sleep(100 * time.Millisecond)
    elapsed3 := time.Since(start3)
    log.Printf("\nTook %s", elapsed3)

}

输出:

My StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy String2009/11/10 23:00:00 
Took 0
My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2My String 22009/11/10 23:00:00 
Took 0
2009/11/10 23:00:00 
Took 100ms

Program exited.

Answer 1

两者编译后的代码没有区别，所以应该不会影响你的结果。以下面的示例文件为例:

package foo

func foo() string {
    x := "Foo"
    return x
}

const MY_STRING = "Bar"

func bar() string {
    x := MY_STRING
    return x
}

汇编器输出显示这两个函数相同(模不同的字符串常量):

$ go tool 6g -S foo.go

--- prog list "foo" ---
0000 (foo.go:3) TEXT    foo+0(SB),$0-16
0001 (foo.go:3) FUNCDATA $0,gcargs·0+0(SB)
0002 (foo.go:3) FUNCDATA $1,gclocals·0+0(SB)
0003 (foo.go:3) TYPE    ~anon0+0(FP){string},$16
0004 (foo.go:4) LEAQ    go.string."Foo"+0(SB),BX
0005 (foo.go:4) MOVQ    (BX),CX
0006 (foo.go:4) MOVQ    8(BX),BP
0007 (foo.go:5) MOVQ    CX,~anon0+0(FP)
0008 (foo.go:5) MOVQ    BP,~anon0+8(FP)
0009 (foo.go:5) RET     ,

--- prog list "bar" ---
0010 (foo.go:10) TEXT    bar+0(SB),$0-16
0011 (foo.go:10) FUNCDATA $0,gcargs·1+0(SB)
0012 (foo.go:10) FUNCDATA $1,gclocals·1+0(SB)
0013 (foo.go:10) TYPE    ~anon0+0(FP){string},$16
0014 (foo.go:11) LEAQ    go.string."Bar"+0(SB),BX
0015 (foo.go:11) MOVQ    (BX),CX
0016 (foo.go:11) MOVQ    8(BX),BP
0017 (foo.go:12) MOVQ    CX,~anon0+0(FP)
0018 (foo.go:12) MOVQ    BP,~anon0+8(FP)
0019 (foo.go:12) RET     ,

如您所见，字符串常量在两种情况下的加载方式相同。