Nested closures

nested.swift

import Foundation

class Closureception {

    deinit {
        print("⚠️ Deallocated")
    }

    // MARK: - Cases

    func retainCycle() {

        self.outer { [weak self] in

            guard let self = self else { return print("👽 self already deallocated, sorry, ciao") }

            print(self.sayHi(to: "Julian"))

            self.inner(name: "Alex") {
                print("👻 Retaining self strongly. And you call yourself iOS developer?...")
                print(self.sayHi(to: $0))
            }

        }

    }

    func rightWay() {

        self.outer { [weak self] in

            guard let self = self else { return print("👽 self already deallocated, sorry, ciao") }

            print(self.sayHi(to: "Julian"))

            self.inner(name: "Alex") { [weak self] in
                guard let self = self else { return print("☠️ self deallocated ages ago, go away!") }
                print(self.sayHi(to: $0))
            }

        }

    }

    // MARK: - Helpers

    private func outer(closure: @escaping () -> Void) { closure() }

    private func inner(name: String, closure: @escaping (String) -> Void) {
        DispatchQueue.main.asyncAfter(deadline: .now() + 2.0) { closure(name) }
    }

    private func sayHi(to name: String) -> String {
        return "Hi \(name) 👋"
    }

}

// MARK: - Test

print("-------------------- Nasty retain cycle ------------------------\n")

var testRetainCycle: Closureception? = Closureception()

testRetainCycle?.retainCycle()
testRetainCycle = nil
print("💥 Should be deallocated!")


DispatchQueue.main.asyncAfter(deadline: .now() + 5.0) {

    print("\n-------------------- Time for the right one -----------------\n")

    var testRightWay: Closureception? = Closureception()

    testRightWay?.rightWay()
    testRightWay = nil
    print("💥 Should be deallocated!")

}

Output

-------------------- Nasty retain cycle ------------------------

Hi Julian 👋
💥 Should be deallocated!
👻 Retaining self strongly. And you call yourself iOS developer?...
Hi Alex 👋
⚠️ Deallocated

-------------------- Time for the right one -----------------

Hi Julian 👋
⚠️ Deallocated
💥 Should be deallocated!
☠️ self deallocated ages ago, go away!