Go to string constants

Question

Is there a difference between the inline string and the constant string used in Go, or is it fully optimized by the compiler?

Example reference code with iterations 100B:

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)

}

Output:

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

There is no difference between the compiled code between them, so it should not affect your results. Take the following example file:

package foo

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

const MY_STRING = "Bar"

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

The assembler output shows that the two functions are the same (modulo different string constants):

$ 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     ,

As you can see, the string constant loads the same in both cases.

Answer 2

. , , . Go, .

,

go tool 6g -S main.go

Answer 3

Well, the problem was not in the code, but it has something to do with http://golang.org/ , and they are how they execute web code. Locally, it seemed faster to use string constants:

> go run bench_string_constant_golang.go

My StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy Strin
gMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy Stri
ngMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy Str
ingMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy St
ringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy S
tringMy 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 StringM
y StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy String
My StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy Strin
gMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy Stri
ngMy StringMy String2014/02/12 12:07:21
Took 1.6400938s

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 Str
ing 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 2M
y String 2My String 2My String 2My String 2My String 2My String 2My String 2My S
tring 2My String 2My String 2My String 2My String 2My String 2My String 2My Stri
ng 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 St
ring 2My String 2My String 2My String 2My String 2My String 2My String 2My Strin
g 2My String 2My String 2My String 2My String 2My String 2My String 2My String 2
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 Str
ing 2My String 2My String 2My String 2My String 2My String 22014/02/12 12:07:23
Took 1.6220928s

2014/02/12 12:07:23
Took 100.0057ms