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53 lines
2.0 KiB
53 lines
2.0 KiB
//
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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 delegate helper type to "shadow" weak `self`, to prevent creating an unexpected retain cycle.
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class Delegate<Input, Output> {
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init() {}
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private var block: ((Input) -> Output?)?
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func delegate<T: AnyObject>(on target: T, block: ((T, Input) -> Output)?) {
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// The `target` is weak inside block, so you do not need to worry about it in the caller side.
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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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func call(_ input: Input) -> Output? {
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return block?(input)
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}
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}
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extension Delegate where Input == Void {
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// To make syntax better for `Void` input.
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func call() -> Output? {
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return call(())
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}
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}
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