Template specialization of a single method from templated class with multiple template parameters

Question

I'm basically trying to do what was discussed in Template specialization of a single method from a templated class except that my TClass has multiple template Parameters like this:

template < class KEY, class TYPE >
class TClass
{
public:
    :
    void doSomething(KEY * v);
    :
};

template < class KEY, class TYPE >
void TClass<KEY, TYPE>::doSomething(KEY * v) 
{
    // do something
}

This works so far, but how do I define a specialized implementation for one template Parameter? I tried adding this:

template < class TYPE >
void TClass<int, TYPE>::doSomething(int * v)
{
    // do something if KEY is int
}

but the Compiler complains about "unable to match function Definition to an existing declaration" (VC2010) for that method/function.

As a sidenote: If I specialize both template Parameters at the same time, it works:

template < >
void TClass<int, char>::doSomething(int * v)
{
    // do something if KEY is int and TYPE is char
}

but that's not what I want to do.

Any suggestions?

Btw, the error messages from VS2015 can be wildly unhelpful. C3860: wrong template parameter order, and C2995: template already defined. — Mark Storer

0x499602D2 0x499602D2 · Accepted Answer · 2013-05-27T19:24:07

You have to specialize the entire class before you define a method through a partial specialization:

template <typename T, typename U>
class TClass;

template <typename T>
class TClass<int, T>
{
    void doSomething(int* v);
};

template <typename T>
void TClass<int, T>::doSomething(int* v)
{
    // ...
}

Live demo

Template specialization of a single method from templated class with multiple template parameters

2 Answers