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* translation: Translate CRTP to zh(Chinese) * translation: Translate CRTP to zh(Chinese)
135 lines
4.0 KiB
Markdown
135 lines
4.0 KiB
Markdown
---
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title: Curiously Recurring Template Pattern
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language: zh
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category: Structural
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tag:
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- Extensibility
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- Instantiation
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---
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## 名称/分类
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Curiously Recurring Template Pattern，CRTP，奇异递归模板模式
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## 别名
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递归类型绑定，递归泛型
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## 目的
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允许派生组件从与派生类型兼容的基本组件继承某些功能。
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## 解释
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真实世界的例子
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> 对于正在策划赛事的综合格斗推广活动来说，确保在相同重量级的运动员之间组织比赛至关重要。这样可以防止体型明显不同的拳手之间的不匹配，例如重量级拳手与雏量级拳手的对决。
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用通俗的话来讲
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> 使类型中的某些方法接受特定于其子类型的参数。
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维基百科介绍
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> 奇异递归模板模式（curiously recurring template pattern，CRTP）是C++模板编程时的一种惯用法：其中类X派生自使用X本身作为模板参数的类模板实例化。
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**程序示例**
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让我们来定义通用接口Fighter
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```java
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public interface Fighter<T> {
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void fight(T t);
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}
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```
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MmaFighter类用于实例化按重量级别区分的拳手
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``` Java
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public class MmaFighter<T extends MmaFighter<T>> implements Fighter<T> {
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private final String name;
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private final String surname;
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private final String nickName;
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private final String speciality;
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public MmaFighter(String name, String surname, String nickName, String speciality) {
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this.name = name;
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this.surname = surname;
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this.nickName = nickName;
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this.speciality = speciality;
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}
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@Override
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public void fight(T opponent) {
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LOGGER.info("{} is going to fight against {}", this, opponent);
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}
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@Override
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public String toString() {
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return name + " \"" + nickName + "\" " + surname;
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}
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```
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以下是 MmaFighter 的一些子类型
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```Java
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class MmaBantamweightFighter extends MmaFighter<MmaBantamweightFighter> {
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public MmaBantamweightFighter(String name, String surname, String nickName, String speciality) {
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super(name, surname, nickName, speciality);
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}
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}
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public class MmaHeavyweightFighter extends MmaFighter<MmaHeavyweightFighter> {
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public MmaHeavyweightFighter(String name, String surname, String nickName, String speciality) {
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super(name, surname, nickName, speciality);
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}
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}
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```
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允许拳手与相同重量级的对手交手，如果对手是不同重量级，则会出现错误
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``` Java
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MmaBantamweightFighter fighter1 = new MmaBantamweightFighter("Joe", "Johnson", "The Geek", "Muay Thai");
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MmaBantamweightFighter fighter2 = new MmaBantamweightFighter("Ed", "Edwards", "The Problem Solver", "Judo");
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fighter1.fight(fighter2); // This is fine
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MmaHeavyweightFighter fighter3 = new MmaHeavyweightFighter("Dave", "Davidson", "The Bug Smasher", "Kickboxing");
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MmaHeavyweightFighter fighter4 = new MmaHeavyweightFighter("Jack", "Jackson", "The Pragmatic", "Brazilian Jiu-Jitsu");
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fighter3.fight(fighter4); // This is fine too
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fighter1.fight(fighter3); // This will raise a compilation error
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```
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## 类图
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## 适用性
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在以下情况下使用CRTP
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* 在对象层次结构中链接方法时存在类型冲突
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* 您想使用一个参数化的类方法，该方法可以接受类的子类作为参数，从而可以应用于继承自类的对象
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* 您希望某些方法仅适用于相同类型的实例，例如实现相互比较。
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## 教程
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* [The NuaH Blog](https://nuah.livejournal.com/328187.html)
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* Yogesh Umesh Vaity answer to [What does "Recursive type bound" in Generics mean?](https://stackoverflow.com/questions/7385949/what-does-recursive-type-bound-in-generics-mean)
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## 已知用途
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* [java.lang.Enum](https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/Enum.html)
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## 鸣谢
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* [How do I decrypt "Enum<E extends Enum\<E>>"?](http://www.angelikalanger.com/GenericsFAQ/FAQSections/TypeParameters.html#FAQ106)
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* Chapter 5 Generics, Item 30 in [Effective Java](https://www.amazon.com/gp/product/0134685997/ref=as_li_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=0134685997&linkCode=as2&tag=javadesignpat-20&linkId=4e349f4b3ff8c50123f8147c828e53eb)
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