Template type check C++

Question

I have a template function which takes in objects. I need to determine whether the object is derived from a particular base class. If it is derived from the base class, I ne

Answer 1

It is somewhat difficult to mix templates and inheritance.

The trouble:

template 
void function(T const& t);

void function(A const& a);

If you use struct B: A {}:, then the template version is preferred, because no conversion is required, and it is therefore a "better" match.

If you have access to the definition of the template version, you can use a combination of is_base_of and disable_if.

template 
typename boost::disable_if< boost::is_base_of >::type function(T const& t);

This simple modification makes use of SFINAE, basically it generates an error when trying to instantiate function for any class derived from A and the C++ standard specifies that if a function may not be instantiated then it is to be removed from the set of overloads considered without triggering a compiler error.

If you do not have access to the template definition of function, you're out of luck.