如何阅读模板的部分专业化知识? [英] How to read the template partial specialization?

问题描述

假设以下声明:

template <typename T> struct MyTemplate;

以下对部分专业化的定义似乎使用相同的字母T来表示不同的类型.

The following definition of the partial specialization seems to use the same letter T to refer to different types.

template <typename T> struct MyTemplate<T*> {};

例如，让我们进行具体的实例化:

For example, let's take a concrete instantiation:

MyTemplate<int *> c;

现在，再次考虑部分专业化的上述定义:

Now, consider again the above definition of the partial specialization:

template <typename T> struct MyTemplate<T*> {};

在此行的第一部分(即template <typename T>)中，T是int *.在该行的第二部分(即MyTemplate<T*>)中，T是int！

In the first part of this line (i.e. template <typename T>), T is int *. In the second part of the line (i.e. MyTemplate<T*>), T is int!

那么，如何理解部分专业化的定义?

So, how is the definition of the partial specialization read?

推荐答案

像这样阅读:

1. 主模板说:"MyTemplate是具有一个类型参数的类模板":

1. The primary template says "MyTemplate is a class template with one type parameter":

template <typename> struct MyTemplate;

部分专业化说，只要类型为T，就存在" ...

The partial specialization says, "whenever there exists a type T"...

template <typename T>

...这样，对于类型T *"...

... such that a specialization of MyTemplate is requested for the type T *"...

struct MyTemplate<T *>

...然后使用此模板的替代定义.

... then use this alternative definition of the template.

您还可以定义显式专业化.例如，可以说当X类型要求专业化时，请使用以下替代定义:

You could also define explicit specializations. For example, could say "whenever the specialization is requested for type X, use this alternative definition:

template <> struct MyTemplate<X> { /* ... */ };

请注意，类模板的显式专业化定义类型，而部分模板化的专业化定义模板.

Note that explicit specializations of class templates define types, wheras partial specializations define templates.

以另一种方式查看:部分类模板专门化推断或 pattern-matches ，类模板参数的结构:

To see it another way: A partial class template specialization deduces, or pattern-matches, the structure of the class template arguments:

template <typename T> struct MyTemplate<T *>
//       ^^^^^^^^^^^^                  ^^^^^
//       This is a new template        Argument passed to the original class
//                                     template parameter

此新模板的参数名称在结构上与原始类模板的参数的参数匹配.

The parameter names of this new template are matched structurally against the argument of the original class template's parameters.

示例:

• MyTemplate<void>:类模板的类型参数为void，主要模板用于此专业化.

• MyTemplate<void>: The type parameter of the class template is void, and the primary template is used for this specialization.

MyTemplate<int *>:类型参数为int *.存在类型T，即T = int，这样所请求的类型参数为T *，因此将模板的部分专业化的定义用于此专业化.

MyTemplate<int *>: The type parameter is int *. There exists a type T, namely T = int, such that the requested type parameter is T *, and so the definition of the partial specialization of the template is used for this specialization.

MyTemplate<X>:参数类型为X，并且已为该参数类型定义了显式专业化，因此将其使用.

MyTemplate<X>: The parameter type is X, and an explicit specialization has been defined for that parameter type, which is therefore used.

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