c++ - 没有<>的模板方法实现

Question

我在类中有一个模板方法:

template<class T>
    A& doSomething(T value)

然后我有一个实现

template<class T>
    A& A::doSomething(T value){
        // do something with value
        return *this;
    }

然后我有一个特化让我们说 bool

template<>
    A& A::doSomething(bool value){
        // do something special with value of type bool
        return *this
    }

这就是我的理解，现在在代码中有这样的东西，我不知道是什么意思:

template A& A::doSomething(char const*);
template A& A::doSomething(char);
template A& A::doSomething(int);
template A& A::doSomething(int*);
template A& A::doSomething(double);
...

模板最后 5 行的确切含义是什么？

谢谢

Answer 1

是Explicit instantiation ，它强制使用指定的模板参数实例化模板，并阻止它们的隐式实例化。

An explicit instantiation definition forces instantiation of the function or member function they refer to. It may appear in the program anywhere after the template definition, and for a given argument-list, is only allowed to appear once in the program.

An explicit instantiation declaration (an extern template) prevents implicit instantiations: the code that would otherwise cause an implicit instantiation has to use the explicit instantiation definition provided somewhere else in the program.

并查看 Explicit instantiation - when is it used?

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^{因为您标记了 c++03，请注意链接页面中提到的 extern template 是从 c++11 引入的。}