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 some OS-specific checks further in code.
func test() (response string) {
if runtime.GOOS != "linux" {
return nil
} else {
/* blablabla*/
}
}
however when I try to compile this code I get an error:
test.go:10:3: cannot use nil as type string in return argument.
If I return just an empty string like return "", I cannot compare this return value with nil further in code.
So the question is how to return a correct nil string value?
Thank you.
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?
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