ameyamashiro / delegated

👷‍♀️ Closure-based delegation without memory leaks

Delegated 2.0

Delegated is a super small package that helps you avoid retain cycles when using closure-based delegation.

New Medium post here.

Original Medium post (Delegated 0.1.2) here.

🚨 WARNING! Delegated 2.0 is not compatible with Delegated 0.1.2. If you don't want to migrate your current codebase, stay on Delegated 0.1.2. See documentation for Delegated 0.1.2 here. If you need any help migrating from 0.1.x to 2.0.x, please open an issue.

Usage

Before:

final class TextField {
    var didUpdate: (String) -> () = { _ in }
}

// later...

self.textField.didUpdate = { [weak self] text in
    guard let strongSelf = self else {
        return
    }
    strongSelf.label.text = text
}

After:

final class TextField {
    @Delegated var didUpdate: (String) -> ()
}

// later...

textField.$didUpdate.delegate(to: self) { (self, text) in
    // `self` is weak automatically!
    self.label.text = text
}

No retain cycles! No memory leaks! No [weak self]! 🎉

Guide

Creating a delegated function

final class TextField {
    @Delegated var didUpdate: (String) -> ()
}

This will only compile for closures that have exactly one argument and no return value. To use any other number of arguments, use this:

final class TextField {
    @Delegated0 var didStartEditing: () -> Void
    @Delegated1 var didUpdate: (String) -> Void
    @Delegated2 var didReplace: (String, String) -> Void
}

Delegated0 - Delegated4 are provided out of the box. Delegated is a typealias for Delegated1.

Registering as a delegate

// somewhere inside init() or viewDidLoad() or similar
self.textField = TextField()
textField.$didUpdate.delegate(to: self) { (self, text) in
    self.label.text = text
}

By default, delegate(to:with:) will wrap self in a weak reference so that you don't need to remember to write [weak self] every time. This is the main feature of Delegated, but if this is not the behavior you want, you can use manuallyDelegate(with:):

// somewhere inside init() or viewDidLoad() or similar
self.textField = TextField()
textField.$didUpdate.manuallyDelegate { (text) in
    print(text)
}

Calling a delegate

final class TextField {
    @Delegated var didUpdate: (String) -> Void
    
    /// ...
    
    private func didFinishEditing() {
        self.didUpdate(self.text)
    }
}

Delegating a function with a return value

If your delegated function is designed to have a return value (non-Void), use @ReturningDelegated wrapper.

final class TextField {
    @ReturningDelegated  var shouldReturn: (String) -> Bool?
    
    @ReturningDelegated0 var shouldBeginEditing: () -> Bool?
    @ReturningDelegated2 var shouldReplace: (String, String) -> Bool?
}

// ...

textField.$shouldReturn.delegate(to: self) { (self, string) -> Bool in
    if string.count > 5 {
        return true
    } else {
        return false
    }
}

IMPORTANT: Make sure that your @ReturningDelegated function returns an optional. It will return nil if no delegate is set.

Default @ReturningDelegated supports exactly one input argument. Use @ReturningDelegated0 - @ReturningDelegated4 if you need a different number of arguments (see above).

Removing a delegate

@Delegated var didUpdate: (String) -> ()
// ...
self.$didUpdate.removeDelegate()

Installation

Swift Package Manager

Delegated is officially available only via Swift Package Manager.

In Xcode 11 or greater, in you project, select: File > Swift Packages > Add Pacakage Dependency

In the search bar type

https://github.com/dreymonde/Delegated

and when you find the package, with the next button you can proceed with the installation.

If you can't find anything in the panel of the Swift Packages you probably haven't added yet your github account. You can do that under the Preferences panel of your Xcode, in the Accounts section.

For command-line based apps, you can just add this directly to your Package.swift file:

dependencies: [
    .package(url: "https://github.com/dreymonde/Delegated", from: "2.1.0"),
]

Manual

Of course, you always have an option of just copying-and-pasting the code - Delegated is just one file, so feel free.