为什么C＃泛型中的专业化有限？ [英] Why is specialization in C# generics limited?

问题描述

什么是具体化？ 对C＃的泛型有一个评论：

通过使用反射检查类型参数，可以维护类型信息，该类型信息允许特化达到某个程度。但是，特殊化程度是有限的，这是由于泛型类型定义在发生任何泛化之前编译的结果（这是通过针对类型参数的约束编译定义来完成的 - 因此，即使没有特定类型参数，编译器也必须能够理解定义）。

• 专业化意味着什么？它是否与具有特定类型参数的泛型类型的实例化不同？

专业化程度有限是什么意思？ / b>


• 为什么它是在泛化发生之前编译泛型类型定义的结果？

解决方案

专业化意味着什么？它与具有特定类型参数的泛型类型的实例化不同？

作者在他的答案的部分内容中解释了致力于Java泛型

泛型类型的特化[是]针对任何特定泛型参数组合使用专用源代码的能力。

换句话说，如果泛型类型参数是特定类型的参数，那么这是一种特殊的功能。当您将类型实例化为 List< bool> 时，为 List List < / code>将是一个专业化的例子。

专业化程度有限是什么意思？

作者的意思是，尽管你可以写一些东西，如



  if （typeof（T）== typeof（bool））{
 ... 
} 
  

响应类型参数组合的能力是有限的，因为任何关于类型组合的决定都必须在运行时作出。



为什么它是在通用化类型定义发生之前编译的事实的结果？

因为在CLR中完成了泛化，所以在C＃编译器不在图片之后。编译器必须为CLR生成一个通用类型定义，作为用于为泛型类实例生成封闭构造类型的模板。

The question "What is reification?" has a comment on C#'s generics:

Type information is maintained, which allows specialization to an extent, by examining type arguments using reflection. However, the degree of specialization is limited, as a result of the fact that a generic type definition is compiled before any reification happens (this is done by compiling the definition against the constraints on the type parameters - thus, the compiler has to be able "understand" the definition even in the absence of specific type arguments).

• What does it mean by "specialization"? Is it not the same as instantiation of a generic type with a specific type argument?

• What does it mean by "the degree of specialization is limited"?

• Why is it "a result of the fact that a generic type definition is compiled before any reification happens"?

解决方案

What does it mean by "specialization"? Is it not the same as instantiation of a generic type with a specific type argument?

Author explains in the portion of his answer dedicated to Java generics that

specialization of a generic type [is] the ability to use specialized source code for any particular generic argument combination.

In other words, it is an ability to do something special if a generic type parameter is of a specific type. Supplying an implementation of List<T> that represents individual elements as bits when you instantiate the type as List<bool> would be an example of specialization.

What does it mean by "the degree of specialization is limited"?

Author means that although you can write things like

if (typeof(T) == typeof(bool)) {
    ...
}

your abilities to respond to a combination of type arguments are limited, because any decision on a type combination has to be made at run-time.

Why is it "a result of the fact that a generic type definition is compiled before any reification happens"?

Because reification is done in CLR, well after C# compiler is out of the picture. The compiler must produce a generic type definition for CLR to use as a "template" for making closed constructed types for instances of a generic class.

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