Explicit specialization in non-namespace scope

Question

template<typename T>
class CConstraint
{
public:
    CConstraint()
    {
    }

    virtual ~CConstraint()
    {
    }

    template <typename TL>
    void Verify(int position, int constraints[])
    {       
    }

    template <>
    void Verify<int>(int, int[])
    {   
    }
};

Compiling this under g++ gives the following error:

Explicit specialization in non-namespace scope 'class CConstraint'

In VC, it compiles fine. Can anyone please let me know the workaround?

Answer 1

VC++ is non-compliant in this case - explicit specializations have to be at namespace scope. C++03, ยง14.7.3/2:

An explicit specialization shall be declared in the namespace of which the template is a member, or, for member templates, in the namespace of which the enclosing class or enclosing class template is a member.
An explicit specialization of a member function, member class or static data member of a class template shall be declared in the namespace of which the class template is a member.

Additionally you have the problem that you can't specialize member functions without explicitly specializing the containing class due to C++03, ยง14.7.3/3, so one solution would be to let Verify() forward to a, possibly specialized, free function:

namespace detail {
    template <typename TL> void Verify     (int, int[]) {}
    template <>            void Verify<int>(int, int[]) {}
}

template<typename T> class CConstraint {
    // ...
    template <typename TL> void Verify(int position, int constraints[]) {
        detail::Verify<TL>(position, constraints);
    }
};