4.5/STL_Extension/STL_Extension_2Default_8cpp-example.html

#include <CGAL/Default.h>

#include <CGAL/use.h>


// A is a concrete type

struct A {};


void use_a(A) {}


// B is the template class which has 2 template parameters

// with default arguments : A and int.

template < typename A1_ = A, typename A2 = int >

struct B

{

    B()

      : a1()

    {}


    // Note that it is also possible to use CGAL::Default

    // instead of A as the default argument for A1_ above.


    // Extract the desired type for A1 :

    typedef typename CGAL::Default::Get<A1_, A>::type  A1;


    A1 a1;

};


int main ()

{

    B<CGAL::Default, double> b;


    use_a(b.a1); //  It is really of type A.

}