[/ 
  Copyright 2007 John Maddock.
  Distributed under the Boost Software License, Version 1.0.
  (See accompanying file LICENSE_1_0.txt or copy at
  http://www.boost.org/LICENSE_1_0.txt).
]

[section:extent extent]
   template <class T, std::size_t N = 0>
   struct extent : public __integral_constant<std::size_t, EXTENT(T,N)> {};
  
__inherit Class template extent inherits from `__integral_constant<std::size_t, EXTENT(T,N)>`, 
where `EXTENT(T,N)` is the number of elements in the N'th array dimension of type `T`.

If `T` is not a (built-in) array type, or if `N > __rank<T>::value`, or if the N'th array bound
is incomplete, then `EXTENT(T,N)` is zero.

__header ` #include <boost/type_traits/extent.hpp>` or ` #include <boost/type_traits.hpp>`

__examples

[:`extent<int[1]>` inherits from `__integral_constant<std::size_t, 1>`.]

[:`extent<double[2][3][4], 0>::type` is the type `__integral_constant<std::size_t, 2>`.]

[:`extent<double[2][3][4], 1>::type` is the type `__integral_constant<std::size_t, 3>`.]

[:`extent<double[2][3][4], 3>::type` is the type `__integral_constant<std::size_t, 4>`.]

[:`extent<int[4]>::value` is an integral constant 
expression that evaluates to /4/.]

[:`extent<int[][2]>::value` is an integral constant 
expression that evaluates to /0/.]

[:`extent<int[][2], 1>::value` is an integral constant 
expression that evaluates to /2/.]

[:`extent<int*>::value` is an integral constant 
expression that evaluates to /0/.]

[:`extent<boost::array<int, 3> >::value` is an integral constant 
expression that evaluates to /0/: `boost::array` is a class type and [*not an array type]!]

[:`extent<T>::value_type` is the type `std::size_t`.]

[endsect]