blog: jl_signal, code: template with function type parameter

gistfile1.cpp

// Forward-declare an empty template class
template< typename SomeFunctionType >
class Signal;

// Specialize the above with a function type and trivially inherit
// from the signal class with the arity in the typename.
template< typename ReturnType, typename P1, typename P2 >
class Signal< ReturnType(P1, P2) > : public Signal2< P1, P2 >
{
    // Nothing required in here. But since this is not exactly
    // the same type as its parent, you might want to implement
    // copy constructors that can translate the parent type to
    // the derived type, and vice-versa.
};