只接受某些类型的C ++模板 [英] C++ templates that accept only certain types

问题描述

在Java中，您可以定义只接受扩展所选类型的类的泛型类，例如：

In Java you can define generic class that accept only types that extends class of your choice, eg:

public class ObservableList<T extends List> {
  ...
}

。

在C ++中有一个简单的等价于这个关键字吗？

Is there some simple equivalent to this keyword in C++?

推荐答案

我建议使用Boost的 static assert 功能与 is_base_of ：

I suggest using Boost's static assert feature in concert with is_base_of from the Boost Type Traits library:

template<typename T>
class ObservableList {
    BOOST_STATIC_ASSERT((is_base_of<List, T>::value)); //Yes, the double parentheses are needed, otherwise the comma will be seen as macro argument separator
    ...
};

在其他一些更简单的情况下，您可以简单地向前声明一个全局模板，显式或部分专门化）它的有效类型：

In some other, simpler cases, you can simply forward-declare a global template, but only define (explicitly or partially specialise) it for the valid types:

template<typename T> class my_template;     // Declare, but don't define

// int is a valid type
template<> class my_template<int> {
    ...
};

// All pointer types are valid
template<typename T> class my_template<T*> {
    ...
};

// All other types are invalid, and will cause linker error messages.

[Minor EDIT 6/12/2013：Using an declared- but-not-defined模板将导致 链接器，而不是编译器，错误消息。]

[Minor EDIT 6/12/2013: Using a declared-but-not-defined template will result in linker, not compiler, error messages.]

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