I have a class to evaluate set algebra but wish to template it.

At the minute it looks a bit like this

set.h:

template<typename T>
  class SetEvaluation
  {
  public:
    SetEvaluation<T>();

    std::set<T>
    evaluate(std::string in_expression);
   }

set.cpp

template<typename T>
   std::set<T>
   SetEvaluation<T>::evaluate(std::string expression)
   {
     std::set<T> result;
     etc etc...
   }

But i'm getting undefined reference errors when compiling.

Is it possible to declare the return type as std::set<T> and then pass std::string as the class template param.

There are no errors in the class but only when I try to instantiate SetEvaluation<std::string>

Can anyone shed light on this problem?

thanks