How to Return Nil String in Go?

Question

I have a function which returns a string under certain circumstances, namely when the program runs in Linux or MacOS, otherwise the return value should be nil in order to omit s

Answer 1

If you can't use "", return a pointer of type *string; or–since this is Go–you may declare multiple return values, such as: (response string, ok bool).

Using *string: return nil pointer when you don't have a "useful" string to return. When you do, assign it to a local variable, and return its address.

func test() (response *string) {
    if runtime.GOOS != "linux" {
        return nil
    } else {
        ret := "useful"
        return &ret
    }
}

Using multiple return values: when you have a useful string to return, return it with ok = true, e.g.:

return "useful", true

Otherwise:

return "", false

This is how it would look like:

func test() (response string, ok bool) {
    if runtime.GOOS != "linux" {
        return "", false
    } else {
        return "useful", true
    }
}

At the caller, first check the ok return value. If that's true, you may use the string value. Otherwise, consider it useless.

Also see related questions:

How do I represent an Optional String in Go?

Alternatives for obtaining and returning a pointer to string: How do I do a literal *int64 in Go?