internal::int2type< N > Struct Template Reference

#include <deal.II/base/template_constraints.h>

Detailed Description

template<int N>
struct internal::int2type< N >

A type that is sometimes used for template tricks. For example, in some situations one would like to do this:

template <int dim>
class X {
  // do something on subdim-dimensional sub-objects of the big
  // dim-dimensional thing (for example on vertices/lines/quads of
  // cells):
  template <int subdim> void f();
};

template <int dim>
template <>
void X<dim>::f<0> () { ...operate on the vertices of a cell... }

template <int dim, int subdim> void g(X<dim> &x) {
  x.f<subdim> ();
}

The problem is: the language doesn't allow us to specialize X::f() without specializing the outer class first. One of the common tricks is therefore to use something like this:

template <int N> struct int2type {};

template <int dim>
class X {
  // do something on subdim-dimensional sub-objects of the big
  // dim-dimensional thing (for example on vertices/lines/quads of
  // cells):
  void f(int2type<0>);
  void f(int2type<1>);
  void f(int2type<2>);
  void f(int2type<3>);
};

template <int dim>
void X<dim>::f (int2type<0>) { ...operate on the vertices of a cell... }

template <int dim>
void X<dim>::f (int2type<1>) { ...operate on the lines of a cell... }

template <int dim, int subdim> void g(X<dim> &x) {
  x.f (int2type<subdim>());
}

Note that we have replaced specialization of X::f() by overloading, but that from inside the function g(), we can still select which of the different X::f() we want based on the subdim template argument.

Author

Wolfgang Bangerth, 2006

Definition at line 252 of file template_constraints.h.

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The documentation for this struct was generated from the following file:

• deal.II/base/template_constraints.h