在Go中引用字符串文字

Question

In my application I will frequently pass references to a static string. I wish to avoid having Go allocate memory for each call, but I failed to get the address to my string literal.

Why is it not possible to take the address of a string literal (see test1() in the example below)? Have I misunderstood the syntax, or is it a limitation due to the internal workings of Go?

If not possible, what would be the best solution?

test2() works, but will it allocate memory for the var hej each time?
test3() will not allocate any new memory, but I wish to avoid clutter outside the function.

package main

import "fmt"

var konnichiwa = `こんにちは世界`

// Gives the compile error `cannot take the address of "Hello world"`
func test1() (*string) { return &`Hello world` }

// Works fine
func test2() (*string) {
    hej := `Hej världen`
    return &hej
}

func test3() (*string) { return &konnichiwa }

func main(){
    fmt.Println(*test1())
    fmt.Println(*test2())
    fmt.Println(*test3())
}

Thanks for help!

Answer 1

Taking the address of a literal (string, number, etc) is illegal because it has ambiguous semantics.

Are you taking the address of the actual constant? Which would allow the value to be modified (and could lead to a runtime error) or do you want to allocate a new object, copy the constant over and get the address to the new version?

This ambiguity does not exist in the case of test2 since you are dealing with an existing variable of which the semantics are clearly defined. The same would not work if the string was defined as const.

The language spec avoids this ambiguity by explicitly not allowing what you are asking for. The solution is test2. While it is slightly more verbose, it keeps the rules simple and clean.

Of course, every rule has its exceptions, and in Go this concerns composit literals: The following is legal and defined as such in the spec:

func f() interface{} {
    return &struct {
        A int
        B int
    }{1, 2} 
}