How to initialize and use function pointer in Swift

Question

Let's say I have this code snipped in the playground

import UIKit

internal final class TestClass {
    internal final var funcPointer: () -> Void

    init() {
        self.funcPointer = self.func1() //Cannot assign value of type '()' to type '() -> Void'
    }

    internal final func func1() {
        print("func1 is called!")
    }
}

var testClass: TestClass = TestClass()
testClass.funcPointer()

Why do I get the shown error message within the init() method and how to initialize a function pointer correctly?

I have already seen this SO post and this tutorial but anyway I don't get it to work for a (Void) -> Void function...

Did you notice that the answers in the post you linked don't call the function when assigning it to a variable? That was intentional. — molbdnilo
– molbdnilo, Commented May 28, 2019 at 15:22
Nit pick: that's not a function pointer, it's a closure. Closures happen to be implemented using function pointers, although even that's not always the case. — Alexander
– Alexander, Commented May 28, 2019 at 18:58

vadian · Accepted Answer · 2019-05-28 15:39:41Z

3

To assign the closure to the property you have to remove the parentheses

self.funcPointer = self.func1

The subsequent error

self' used in method call 'func1' before all stored properties are initialized

can be fixed by declaring funcPointer implicit unwrapped optional

internal final var funcPointer: (() -> Void)!

answered May 28, 2019 at 15:39

vadian

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1 Comment

Pascal Over a year ago

Could you also answer this question? stackoverflow.com/questions/56348309/… :)

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