为什么函数模板不能被部分专门化？

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我知道语言规范禁止功能模板的部分专业化。

I know the language specification forbids partial specialization of function template.

我想知道为什么它禁止的理由？

I would like to know the rationale why it forbids it? Are they not useful?

template<typename T, typename U> void f() {} //allowed! template<> void f<int, char>() {} //allowed! template<typename T> void f<char, T>() {} //not allowed! template<typename T> void f<T, int>() {} //not allowed!

推荐答案

AFAIK在C ++ 0x 。

我想这只是一个疏忽（考虑到你可以总是获得部分专业化效果与更详细的代码，通过将函数作为 static 一个类的成员）。

I guess it was just an oversight (considering that you can always get the partial specialization effect with more verbose code, by placing the function as a static member of a class).

您可以查找相关的DR（缺陷报告） 。

You might look up the relevant DR (Defect Report), if there is one.

EDIT ：检查这一点，我发现其他人也相信，但没有人能够在标准草案。 此SO线程似乎表明不支持功能模板的部分专门化在C ++ 0x 中。

EDIT: checking this, I find that others have also believed that, but no-one is able to find any such support in the draft standard. This SO thread seems to indicate that partial specialization of function templates is not supported in C++0x.

编辑2 ：只是一个例子， code> static 类的成员：

EDIT 2: just an example of what I meant by "placing the function as a static member of a class":

#include <iostream> using namespace std; // template<typename T, typename U> void f() {} //allowed! // template<> void f<int, char>() {} //allowed! // template<typename T> void f<char, T>() {} //not allowed! // template<typename T> void f<T, int>() {} //not allowed! void say( char const s[] ) { std::cout << s << std::endl; } namespace detail { template< class T, class U > struct F { static void impl() { say( "1. primary template" ); } }; template<> struct F<int, char> { static void impl() { say( "2. <int, char> explicit specialization" ); } }; template< class T > struct F< char, T > { static void impl() { say( "3. <char, T> partial specialization" ); } }; template< class T > struct F< T, int > { static void impl() { say( "4. <T, int> partial specialization" ); } }; } // namespace detail template< class T, class U > void f() { detail::F<T, U>::impl(); } int main() { f<char const*, double>(); // 1 f<int, char>(); // 2 f<char, double>(); // 3 f<double, int>(); // 4 }