问题描述
我有一个模板类和一个模板成员函数:
I have a template class and a template member function:
template<class T1>
struct A{
template<class T2>
static int f(){return 0;}
};
我想专门研究T1
和T2
相同的情况,
I want to specialize for a case when T1
and T2
are the same,
例如,为任何T
定义大小写A<T>::f<T>
.
For example, define the case A<T>::f<T>
for any T
.
但是我找不到关键字的组合来实现这一目标.
but I can't find the combination of keywords to achieve this.
如何部分(?)专门化模板类和模板静态函数的组合?
这些是我的未成功尝试,以及错误消息:
These are my unsuccessful attempts, and the error messages:
1)专攻课程:fatal error: cannot specialize a function 'f' within class scope
)
template<class T1>
struct A{
template<class T2>
static int f(){return 0;}
template<>
static int f<T1>(){return 1;}
};
2)同时"在课外学习:fatal error: cannot specialize a member of an unspecialized template
2) Specialize outside the class "simultaneously": fatal error: cannot specialize a member of an unspecialized template
template<class T>
void A<T>::f<T>(){return 1;}
3)专门使用template<>
:fatal error: too few template parameters in template redeclaration
template<> template<class T>
void A<T>::f<T>(){return 1;}
4)颠倒顺序:fatal error: cannot specialize (with 'template<>') a member of an unspecialized template
template<class T> template<>
void A<T>::f<T>(){return 1;}
5)专业化整个类(基于尝试3的错误):fatal error: class template partial specialization does not specialize any template argument; to define the primary template, remove the template argument list
5) Specialize the whole class (based on the error of attempt 3): fatal error: class template partial specialization does not specialize any template argument; to define the primary template, remove the template argument list
template<class T>
struct A<T>{
template<>
static int f<T>(){return 1;}
};
6)专业化类而不是函数(?):fatal error: too few template parameters in template redeclarationtemplate<> template<class T1>
6) Specialize the class but not the function (?): fatal error: too few template parameters in template redeclarationtemplate<> template<class T1>
template<> template<class T>
int A<T>::f(){return 0;}
我使用clang 3.5 C++14
生成错误消息.
推荐答案
您不能部分专门化一个函数.
You cannot partially specialize a function.
您可以将作品转发到另一种类型:
You can forward the work to another type:
template<class T1>
struct A;
template<class T1, class T2>
struct A_helper {
static int f() {
return A<T1>::f_simple<T2>();
}
};
template<class T>
struct A_helper<T,T> {
static int f() {
return A<T>::f_special();
}
};
template<class T1>
struct A{
template<class T2>
static int f(){return A_helper<T1,T2>::f()}
template<class T2>
static int f_simple(){return 0;}
static int f_special(){return -1;}
};
或更简单地说,没有A_helper
:
template<class T1>
struct A{
template<class T2>
static int f(){return f2<T2>(std::is_same<T1,T2>{});}
template<class T2>
static int f2(std::true_type){
static_assert(std::is_same<T1,T2>{}, "bob!");
return -1;
}
tempalte<class T2>
static int f2(std::false_type){return -1;}
};
您可以使用标签分发.
另一种方法:
template<class T>struct tag{};
template<class T1>
struct A{
template<class T2>
static int f(){return f2(tag<T2>{});}
template<class T2>
static int f2(tag<T2>) {return 0;}
static int f2(tag<T1>) {return -1;}
};
我们直接根据T2
的类型进行调度.
where we directly dispatch on the type of T2
.
这篇关于模板类的静态模板成员函数的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持!