Function references and retain cycles

retain_cycles.swift

class MyClass {
    var foo: () -> Void = {}
    init() {
        foo = defaultFoo
    }
    private func defaultFoo() {
        print("Foo Bar")
    }
    deinit {
        print("MyClass Released 🎉") // Never gets called, retain cycle
    }
}


class MyClassNested {
    var foo: () -> Void = {}
    init() {
        func defaultFoo() {
            print("Foo Bar Nested")
        }
        foo = defaultFoo
    }
    deinit {
        print("MyClassNested Released 🎉") // Gets called
    }
}

var normal: MyClass? = MyClass()
var nested: MyClassNested? = MyClassNested()
normal?.foo() // prints: Foo Bar
nested?.foo() // prints: Foo Bar Nested
normal = nil  // deinit does not get called
nested = nil  // prints: MyClassNested Released 🎉

// Alternatively, this code is simpler, but deinit is called first because the instance is released right away
MyClass().foo() // deinit does not get called
MyClassNested().foo() // deinit gets called