Question

I am having the case in which a function with the following code:

func halfMatch(text1, text2 string) []string {
    ...
    if (condition) {
         return nil // That's the final code path)
    }
    ...
}

is returning []string(nil) instead of nil. At first, I thought that perhaps returning nil in a function with a particular return type would just return an instance of a zero-value for that type. But then I tried a simple test and that is not the case.

Does anybody know why would nil return an empty string slice?

Answer 1

Nil is not a type. It is a description of the zero value for maps, chans, pointers, functions, slices, and interfaces.

When you put “nil” in your program, go gives it a type depending on the context. For the most part, you never need to explicitly type your nil. This is no exception, the compiler knows it must be a []string(nil) because the type returned is []string.

A nil string slice is a slice with no backing array and a length/capacity of zero. You may compare it to the literal “nil” and can get its length and capacity. It is a []string, just empty. If you wish to have an empty []string that is not nil, return []string{}. This creates a backing array (of length zero) and makes it no longer equivalent to nil.