AssociatedObject

Swift Macro for allowing variable declarations even in class extensions. It is implemented by wrapping objc_getAssociatedObject/objc_setAssociatedObject.

Installation

SPM

.package(url:"https://github.com/p-x9/AssociatedObject", from:"0.10.3")

CocoaPods

Add below to your Podfile.

pod 'AssociatedObject', git: 'https://github.com/p-x9/AssociatedObject', tag: '0.10.3'

After pod install, you can use this Macro in your project.

Additionally, if you encounter build error like Expansion of macro 'AssociatedObject' did not produce a non-observing accessor. You should check your project setting Build Settings-OTHER_SWIFT_FLAGS.

There should be additional flags like so.

If not, you can add these two lines by yourself.

-load-plugin-executable
${PODS_ROOT}/AssociatedObject/Binary/AssociatedObjectPlugin#AssociatedObjectPlugin

Usage

For example, you can add a new stored property to UIViewController by declaring the following

import AssociatedObject
extensionUIViewController{@AssociatedObject(.retain(nonatomic))vartext="text"
/* OR */
@AssociatedObject(.OBJC_ASSOCIATION_RETAIN_NONATOMIC)vartext="text"staticvarcustomKey=""@AssociatedObject(.OBJC_ASSOCIATION_RETAIN_NONATOMIC, key: customKey)varsomevar="text"}

Declared properties can be used as follows

classViewController:UIViewController{overridefunc viewDidLoad(){
super.viewDidLoad()print(text) // => "text"
text ="hello"print(text) // => "hello"
}}

willSet/didSet

Properties defined using @AssociatedObject can implement willSet and didSet. In swift, it is not possible to implement willSet and didSet at the same time as setter, so they are expanded as follows.

@AssociatedObject(.copy(nonatomic))publicvarhello:String="こんにちは"{
didSet {print("didSet")}
willSet {print("willSet: \(newValue)")}}
// ↓↓↓ expand to ... ↓↓↓
publicvarhello:String="こんにちは"{get{objc_getAssociatedObject(self,&Self.__associated_helloKey
)as?String??"こんにちは"}set{letwillSet:(String)->Void={[self] newValue inprint("willSet: \(newValue)")}willSet(newValue)letoldValue= hello
objc_setAssociatedObject(self,&Self.__associated_helloKey,
newValue,.copy(nonatomic))letdidSet:(String)->Void={[self] oldValue inprint("didSet")}didSet(oldValue)}}

License

AssociatedObject is released under the MIT License. See LICENSE