133 lines
3.7 KiB
Swift
133 lines
3.7 KiB
Swift
//
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// Delegate.swift
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// Kingfisher
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//
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// Created by onevcat on 2018/10/10.
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//
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// Copyright (c) 2019 Wei Wang <onevcat@gmail.com>
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//
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// Permission is hereby granted, free of charge, to any person obtaining a copy
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// of this software and associated documentation files (the "Software"), to deal
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// in the Software without restriction, including without limitation the rights
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// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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// copies of the Software, and to permit persons to whom the Software is
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// furnished to do so, subject to the following conditions:
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//
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// The above copyright notice and this permission notice shall be included in
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// all copies or substantial portions of the Software.
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//
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// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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// THE SOFTWARE.
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import Foundation
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/// A class that keeps a weakly reference for `self` when implementing `onXXX` behaviors.
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/// Instead of remembering to keep `self` as weak in a stored closure:
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///
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/// ```swift
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/// // MyClass.swift
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/// var onDone: (() -> Void)?
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/// func done() {
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/// onDone?()
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/// }
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///
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/// // ViewController.swift
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/// var obj: MyClass?
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///
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/// func doSomething() {
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/// obj = MyClass()
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/// obj!.onDone = { [weak self] in
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/// self?.reportDone()
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/// }
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/// }
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/// ```
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///
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/// You can create a `Delegate` and observe on `self`. Now, there is no retain cycle inside:
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///
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/// ```swift
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/// // MyClass.swift
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/// let onDone = Delegate<(), Void>()
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/// func done() {
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/// onDone.call()
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/// }
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///
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/// // ViewController.swift
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/// var obj: MyClass?
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///
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/// func doSomething() {
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/// obj = MyClass()
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/// obj!.onDone.delegate(on: self) { (self, _)
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/// // `self` here is shadowed and does not keep a strong ref.
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/// // So you can release both `MyClass` instance and `ViewController` instance.
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/// self.reportDone()
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/// }
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/// }
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/// ```
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///
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public class Delegate<Input, Output> {
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public init() {}
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private var block: ((Input) -> Output?)?
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public func delegate<T: AnyObject>(on target: T, block: ((T, Input) -> Output)?) {
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self.block = { [weak target] input in
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guard let target = target else { return nil }
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return block?(target, input)
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}
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}
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public func call(_ input: Input) -> Output? {
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return block?(input)
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}
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public func callAsFunction(_ input: Input) -> Output? {
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return call(input)
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}
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}
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extension Delegate where Input == Void {
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public func call() -> Output? {
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return call(())
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}
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public func callAsFunction() -> Output? {
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return call()
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}
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}
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extension Delegate where Input == Void, Output: OptionalProtocol {
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public func call() -> Output {
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return call(())
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}
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public func callAsFunction() -> Output {
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return call()
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}
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}
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extension Delegate where Output: OptionalProtocol {
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public func call(_ input: Input) -> Output {
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if let result = block?(input) {
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return result
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} else {
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return Output._createNil
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}
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}
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public func callAsFunction(_ input: Input) -> Output {
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return call(input)
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}
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}
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public protocol OptionalProtocol {
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static var _createNil: Self { get }
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}
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extension Optional : OptionalProtocol {
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public static var _createNil: Optional<Wrapped> {
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return nil
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}
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}
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