Specialization of templated member function in templated class
I have a templated class with an templated member function
template<class T>
class A {
public:
template<class CT>
CT function();
};
Now I want to specialize the templated member function in 2 ways. First for having the same type as the class:
template<class T>
template<> // Line gcc gives an error for, see below
T A<T>::function<T>() {
return (T)0.0;
}
Second for type bool:
template<class T>
template<>
bool A<T>::function<bool>() {
return false;
}
Here is how I am trying to test it:
int main() {
A<double> a;
bool b = a.function<bool>();
double d = a.function<double>();
}
Now gcc gives me for the line marked above:
error: invalid explicit specialization before ‘>’ token
error: enclosing class templates are not explicitly sp开发者_如何学JAVAecialize
So gcc is telling me, that I have to specialize A, if I want to specialize function, right? I do not want to do that, I want the type of the outer class to be open ...
Is the final answer: it is not possible? Or is there a way?
Yes, this is the problem:
error: enclosing class templates are not explicitly specialized
You cannot specialize a member without also specializing the class.
What you can do is put the code from function
in a separate class and specialize that, much like basic_string depends on a separate char_traits class. Then then non-specialized function
can call a helper in the traits class.
You can use overload, if you change the implementation.
template <typename T>
class Foo
{
public:
template <typename CT>
CT function() { return helper((CT*)0); }
private:
template <typename CT>
CT helper(CT*);
T helper(T*) { return (T)0.0; }
bool helper(bool*) { return false; }
};
Simple and easy :)
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