Partial template specialization on a class - c++

Question

I'm looking for a better way to this. I have a chunk of code that needs to handle several different objects that contain different types. The structure that I have looks like this:
class Base
{
// some generic methods
}
template <typename T> class TypedBase : public Base
{
// common code with template specialization
private:
std::map<int,T> mapContainingSomeDataOfTypeT;
}
template <> class TypedBase<std::string> : public Base
{
// common code with template specialization
public:
void set( std::string ); // functions not needed for other types
std::string get();
private:
std::map<int,std::string> mapContainingSomeDataOfTypeT;
// some data not needed for other types
}
Now I need to add some additional functionality that only applies to one of the derivative classes. Specifically the std::string derivation, but the type doesn't actually matter. The class is big enough that I would prefer not copy the whole thing simply to specialize a small part of it. I need to add a couple of functions (and accessor and modifier) and modify the body of several of the other functions. Is there a better way to accomplish this?

Answer 1

Impose another level of indirection in the template definitions:
class Base
{
// Generic, non-type-specific code
};
template <typename T> class TypedRealBase : public Base
{
// common code for template
};
template <typename T> class TypedBase : public TypedRealBase<T>
{
// Inherit all the template functionality from TypedRealBase
// nothing more needed here
};
template <> class TypedBase<std::string> : public TypedRealBase<T>
{
// Inherit all the template functionality from TypedRealBase
// string-specific stuff here
}

Answer 2

You don't have to specialize the whole class, only what you want. Works with GCC & MSVC:
#include <string>
#include <iostream>
class Base {};
template <typename T>
class TypedBase : public Base
{
public:
T get();
void set(T t);
};
// Non-specialized member function #1
template <typename T>
T TypedBase<T>::get()
{
return T();
}
// Non-specialized member function #2
template <typename T>
void TypedBase<T>::set(T t)
{
// Do whatever here
}
// Specialized member function
template <>
std::string TypedBase<std::string>::get()
{
return "Hello, world!";
}
int main(int argc, char** argv)
{
TypedBase<std::string> obj1;
TypedBase<double> obj2;
std::cout << obj1.get() << std::endl;
std::cout << obj2.get() << std::endl;
}