Go lang string constants

Question

Is there a difference between an inline string and a constant string being used in Go, or is this being optimized entirely by the compiler? Example benchmark code with 100B iterations: ``` 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("
Took %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("
Took %s", elapsed2) // Proof that the timer does work :) start3 := time.Now() time.Sleep(100 * time.Millisecond) elapsed3 := time.Since(start3) log.Printf("
Took %s", elapsed3) } ``` Output: ``` My StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy StringMy Str…

Accepted Answer

There is no difference in the compiled code between the two, 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 the 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 is loaded the same way in both cases.

Go lang string constants

Solution

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