.. Sequences/Intrinsic Metafunctions//back

back

Synopsis

.. parsed-literal::

template<
      typename Sequence
    >
struct back
{
    typedef |unspecified| type;
};

Description

Returns the last element in the sequence.

Header

.. parsed-literal::

#include <boost/mpl/back.hpp>

Model of

|Tag Dispatched Metafunction|

Parameters

+---------------+---------------------------+-----------------------------------+ | Parameter | Requirement | Description | +===============+===========================+===================================+ | Sequence | |Bidirectional Sequence| | A sequence to be examined. | +---------------+---------------------------+-----------------------------------+

Expression semantics

For any |Bidirectional Sequence| s:

.. parsed-literal::

typedef back<s>::type t; 

:Return type: A type.

:Precondition: empty<s>::value == false.

:Semantics: Equivalent to

.. parsed-literal::

   typedef deref< prior< end<s>::type >::type >::type t;

Complexity

Amortized constant time.

Example

.. parsed-literal::

typedef range_c<int,0,1> range1;
typedef range_c<int,0,10> range2;
typedef range_c<int,-10,0> range3;
    
BOOST_MPL_ASSERT_RELATION( back<range1>::value, ==, 0 );
BOOST_MPL_ASSERT_RELATION( back<range2>::value, ==, 9 );
BOOST_MPL_ASSERT_RELATION( back<range3>::value, ==, -1 );

See also

|Bidirectional Sequence|, |front|, |push_back|, |end|, |deref|, |at|

.. copyright:: Copyright 2001-2009 Aleksey Gurtovoy and David Abrahams 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)