Do ! Or how to 'clean up' code when using `Dispatch.main`+ weak pointer

Dowit.swift

import Foundation


/// #Do class - Or how to transform DispatchQueue-escaping-weakable stuff on pointer into a more readable usage

/// TL;DR - Usage

// In ViewModel/Interactor
Do.bg(on: self) { this in
    this.doSomeWSCalls()
}

// In View(Controller
Do.ui(on: self) { this in
    this.reloadView()
}



/// A nano class which help developer avoid messy code with DispatchQueue and `self` weaked pointer
final class Do {
    
    typealias DoClosure<T> = ((_:T)->()) // just because it's horrible to read

    private init() {}
    
    /// Do it in background thread
    static func bg<T: AnyObject>(on object: T, closure: @escaping DoClosure<T>) {
        weak var _object = object
        DispatchQueue.global(qos: .background).async {
            guard let __obj = _object else { return }
            closure(__obj)
        }
    }
    
    /// Do it in main thread
    static func ui<T: AnyObject>(on object: T, closure: @escaping DoClosure<T>) {
        weak var _object = object
        DispatchQueue.main.async {
            guard let __obj = _object else { return }
            closure(__obj)
        }
    }

}

/// ## From this ...



class MyClass {
    var string: String = "Oh, Hello !"
    func doSomethingOnScreen() {
        DispatchQueue.main.async { [weak self] in
            print(self?.string ?? "borken pointer")
        }
    }
    
    func doSomethingInBackground() {
        DispatchQueue.global(qos: DispatchQoS.QoSClass.background).async { [weak self] in
            self?.string = "Oh, Hello from the background !"
        }
    }
    
}


/// ## ... to this

class MyBetterClass {
    var string: String = "Oh, Hello !"
    func doSomethingOnScreen() {
        Do.ui(on: self) { this in
            print(this.string)
        }
    }
    
    func doSomethingInBackground() {
        Do.bg(on: self) { this in
            this.string = "Oh, Hello from the background ! (But better 😎)"
        }
    }
    
}



/// Usage

class _MyClass {
    var string: String = "Oh, Hello !"
    func doSomethingOnScreen() {
        DispatchQueue.main.async { [weak self] in
            Thread.printCurrentDescription()
            print(self?.string ?? "borken pointer")
            print("Done things in the background.")
        }
    }
    
    func doSomethingInBackground() {
        DispatchQueue.global(qos: DispatchQoS.QoSClass.background).async { [weak self] in
            Thread.printCurrentDescription()
            self?.string = "Oh, Hello from the background !"
            print("Done things in the background.")
        }
    }
    
}

class _MyBetterClass {
    var string: String = "Oh, Hello !"
    func doSomethingOnScreen() {
        Do.ui(on: self) { this in
            Thread.printCurrentDescription()
            print(this.string)
            print("Done things in the background. (But better 😎)")
        }
    }
    
    func doSomethingInBackground() {
        Do.bg(on: self) { this in
            Thread.printCurrentDescription()
            this.string = "Oh, Hello from the background ! (But better 😎)"
        }
    }
    
}



// ⚠️ -- debug print are biased (their order) due to print latency ...

let boringClass = _MyClass()
boringClass.doSomethingInBackground()
do {
    sleep(1)
}
boringClass.doSomethingOnScreen()

do {
    sleep(2)
}

let betterClass = _MyBetterClass()
betterClass.doSomethingInBackground()
do {
    sleep(1)
}
betterClass.doSomethingOnScreen()


/// Just a helper extension 👀
extension Thread {
    class func printCurrentDescription() {
        print("\r⚡️: \(Thread.current)\r" + "🏭: \(OperationQueue.current?.underlyingQueue?.label ?? "None")\r")
    }
}