class template with multiple template parameter

Question

I am trying to define the same template class in several version, each with a different template parameter. The compiler is giving me the error

 previous declaration ‘template<class T1> class A’ used

Is there a way to circumvent this problem? Unfortunately I cannot use Cx++11 where I can assign a default template parameter. What is a good practice to tackle this issue? I am using old g++4.4.7

#include <iostream> template <class T1> class A{}; template <class T1,class T2> class A{}; int main() { return 0; }

Kerrek has the right answer, but C++11 only added default template types to functions... you could always write template <typename T1, typename T2 = void> class A { }; — Barry
– Barry, Commented Nov 21, 2014 at 18:11

Kerrek SB · Accepted Answer · 2014-11-21 18:05:11Z

Make a variadic template and add partial specializations:

template <typename ...> class A; // leave primary template undefined template <typename T> class A<T> { // ... }; template <typename T1, typename T2> class A<T1, T2> { // ... };

Hi Kerrek. Good stuff the partial specialization! Sorry that I can't use variadic templates, but I like the response.

vsoftco · Accepted Answer · 2014-11-21 18:18:08Z

If you cannot use C++11 variadic templates, you can use a "mock" type

struct NoType{}; template <class T1, class T2 = NoType> // or class T2 = void, doesn't really matter class A{};

then specialize it as needed.

PS: as @Barry mentioned in the comment, default template parameters for classes ARE ALLOWED in pre C++11 . The novelty in this respect introduced by C++11 is to allow default template parameters in functions.

Hi. This is ok ..it is meant/works well to be used with Partial Specialization.

Collectives™ on Stack Overflow

class template with multiple template parameter

2 Answers 2

1 Comment

1 Comment

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

1 Comment

Related