swift5.swift

import Foundation

class A {
    init(completion: @escaping () -> Void) {}
}

class B {
    init(a: A) {}
}

class C {
    lazy var a = A { [weak self] in
        guard let self = self else { return }

        self.printB()
        // Uncomment next line and get a compile error
        // debugPrint(self.b)
    }

    lazy var b = B(a: self.a)

    func printB() {
        debugPrint(b)
    }
}