我感觉这个是swift的设计缺陷。
类型擦除：解决泛型类型作为公用类型的问题
是抽象的公用机制的一种实现方式。
1）类型擦除并不能解决类型不一致的兼容问题，只能解决类似继承一致性的兼容问题。
2）擦除类型后的抽象类型，其类型信息仍然存在，只是需要保持逻辑一致性。
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import Foundation |
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protocol Pokemon { |
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associatedtype Power |
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func attack() -> Power |
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} |
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struct Pikachu: Pokemon { |
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func attack() -> ?? { |
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return ??() |
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} |
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} |
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struct Charmander: Pokemon { |
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func attack() -> ?? { |
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return ??() |
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} |
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} |
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// power types |
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struct ?? { } |
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struct ?? { } |
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// MARK: - Abstract base class |
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class _AnyPokemonBase<Power>: Pokemon { |
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init() { |
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guard type(of: self) != _AnyPokemonBase.self else { |
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fatalError("_AnyPokemonBase<Power> instances can not be created; create a subclass instance instead") |
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} |
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} |
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func attack() -> Power { |
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fatalError("Must override") |
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} |
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} |
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// MARK: - Box container class |
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fileprivate final class _AnyPokemonBox<Base: Pokemon>: _AnyPokemonBase<Base.Power> { |
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var base: Base |
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init(_ base: Base) { self.base = base } |
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fileprivate override func attack() -> Base.Power { |
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return base.attack() |
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} |
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} |
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// MARK: - AnyPokemon Wrapper |
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final class AnyPokemon<Power>: Pokemon { |
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private let box: _AnyPokemonBase<Power> |
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init<Base: Pokemon>(_ base: Base) where Base.Power == Power { |
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box = _AnyPokemonBox(base) |
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} |
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func attack() -> Power { |
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return box.attack() |
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} |
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} |
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// Use AnyPokemon type directly |
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let pokemon: AnyPokemon = AnyPokemon(Pikachu()) |
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pokemon.attack() |
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// Add a new electric Pokemon |
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class Jolteon: Eevee, Pokemon { |
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func attack() -> ?? { |
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return ??() |
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} |
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} |
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class Eevee {} |
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// Iterate over a collection of Electric Pokemon |
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let electricPokemon = [AnyPokemon(Pikachu()), AnyPokemon(Jolteon())] |
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electricPokemon.map() { $0.attack() } |
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- class Pet { }
- class Dog: Pet { }
- class Cat: Pet { }
- // 1. 隐藏具体宠物类型信息
- let pets: [Pet] = [Dog(), Cat()]
https://github.com/bignerdranch/type-erasure-playgrounds/blob/master/playgrounds/Pokemon_erasure.playground/Contents.swift
原文地址：https://www.cnblogs.com/feng9exe/p/11978823.html
时间： 2024-10-26 16:37:16