Breaking strong reference cycle in closures

breaking_strong_reference_cycle_in_closures.swift

import Foundation

class User {
    var firstName: String
    var lastName: String

    // Comment this to see strong reference cycle
    lazy var fullName: () -> String = {
        [weak self] in
        guard let strongSelf = self else { return "No name specified." }
        return "\(strongSelf.firstName) \(strongSelf.lastName)"
    }
    
    // Uncomment this to see strong reference cycle
    //    lazy var fullName: () -> String = {
    //        return "\(self.firstName) \(self.lastName)"
    //    }
    
    init(firstName: String, lastName: String) {
        self.firstName = firstName
        self.lastName = lastName
        print("\(User.self) \(firstName) \(lastName) initialised.")
    }

    deinit {
        print("Deallocating \(User.self) object.")
    }
}

let fullName: () -> String

// do closure to simulate codes going into and out of scope
do {
    let u = User(firstName: "Johnny", lastName: "English")
    fullName = u.fullName
    
    print(fullName())
}

print(fullName())