Restricting template types: Requiring member functions

It is desired that a class parametrized by, say a single type argument, T, only be instantiated by types that provide a particular function ( say void foo() )

// T must have void T::foo()  

template <class T>   
class RequireFoo   
{   
} 

A petty solution:

template <class T>   
class RequireFoo   
{   
public:   
   ~RequireFoo(){ void (T::*fptr)() = &T::foo; }   
};

The above solution will throw a compiler error if non foo having class is used as a parameter.

A much cooler solution: Move this check out to a template class

template <class T>   
class CheckFoo   
{   
public:   
   CheckFoo(){ void (T::*fptr) = &T::foo; }   
} 
  
template< class T >  
class RequireFoo: CheckFoo<T>   
{   
} 

Here, the responsibility of checking for foo is checked in base class CheckFoo's constructor which is automatically called when RequireFoo is instantiated.
Ideas from: http://www.gotw.ca/publications/mxc++-item-4.htm

Complete Code:

#include <iostream>

class HasFoo
{
public:
  void foo(){}
};

class NoFoo
{
};

template <class T>
class CheckFoo
{
public:
  CheckFoo(){    void (T::*fptr)() = &T::foo;    }
};

template <class T>
class RequireFoo: CheckFoo<T>
{
public:
};

int main()
{
  RequireFoo< HasFoo > t;
  return 0;
}