NoRetainCycle

NoRetainCycle.swift

//: Playground - noun: a place where people can play

import Foundation

prefix operator ~

prefix func ~<Entity, Parameters>(_ param: ((Entity) -> (Parameters) -> (), Entity)) -> WeakCallback<Parameters>
    where Entity: AnyObject
{
    return WeakCallback.weakifyFunction(param.0, object: param.1)
}

class WeakCallback<Parameters> {
    private let innerCallback: (Parameters) -> ()
    
    init(_ f: @escaping (Parameters) -> ()) {
        innerCallback = f
    }
    
    func call(_ parameters: Parameters) {
        innerCallback(parameters)
    }
    
    static func weakifyFunction<Entity>(_ f: @escaping (Entity) -> (Parameters) -> (), object: Entity) -> WeakCallback<Parameters>
        where Entity: AnyObject
    {
        return WeakCallback({ [weak object] (parameters) in
            object.map { f($0)(parameters) }
        })
    }
}

class Base {
    deinit {
        print("\(String(describing: self)) deinitialized")
    }
}

class Processor: Base {
    typealias Callback = (Processor) -> ()
    var callback: WeakCallback<Processor>?
    
    func process() {
        // ... do something
        self.callback?.call(self)
    }
}

class Data: Base {
    
    let processor = Processor()
    
    override init() {
        super.init()
        processor.callback = (~)((Data.onProcessingFinished, self))
    }
    
    func process() {
        self.processor.process()
    }
    
    func onProcessingFinished(processor: Processor) {
        print("procesing complete")
    }
}

var data: Data? = Data()
data?.process()
data = nil