C / C++ / MFC

class CSomeWnd : public CWindowImpl<CSomeWnd>
{ ... };

template <typename T>
class A
{
public:
    A ( T t ) : m_t(t) { }
    T m_t;
};
 
// now declare a variable
A<char> a_obj('x');

class B : public A<int>
{
public:
    B(int n) : A<int>(n) { }
};
 
// now declare a variable:
B b_obj(1);

template <typename T>
class C : public A<T>
{
public:
    C(T t) : A<T>(t) { }
};
 
// now declare a variable:
C<double> c_obj(3.14);  // derives from A<double>

template <typename T, typename U>
class D : public A<T>
{
public:
    D(T t) : A<T>(t), m_u(0) { }
    U m_u;
};
 
// variable:
D<float,int> d_obj(2.71828);  // derives from A<float>