implicit return in a closure causing an error

Question

Error: Cannot convert the expression type (String, MyType) to ()

From the following code

Test(method: {[weak self] (message: String         


        

Answer 1

The implicit return is returning the result of your callback() method. That return value conflicts with the closure's return value of void. You thus need an explicit, if ugly, return.

Answer 2

Not sure how to handle the above without having to have the dummy return statement, any advise.

You have solved the problem beautifully. Anonymous functions automatically use a one-line function body as a return value, so to prevent that from causing a type mismatch with the expected return type (Void) you have to add another line of code so that it is not a one-line function body. The dummy return statement, which itself returns Void, is a great way to handle it; I would just use that and move on. There are some snazzier workarounds but what you have is precisely what I would do.

EDIT: To understand the source of the type mismatch, try this:

struct Test {
    func voider() -> Void {}
}

let testMaybe = Optional(Test())
let result = testMaybe?.voider()

Now result is not a Void; it's an Optional wrapping a Void. That is what's happening to you; a Void is expected but your one-line anonymous function returns an Optional wrapping a Void. By adding another line that returns Void explicitly, you solved the problem.