pop_back

Synopsis

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

Description

pop_back performs a removal at the end of the sequence with guaranteed O(1) complexity.

Header

#include <boost/mpl/pop_back.hpp>

Model of

Tag Dispatched Metafunction

Parameters

Parameter	Requirement	Description
`Sequence`	Back Extensible Sequence	A sequence to erase the last element from.

Expression semantics

For any Back Extensible Sequence s:

typedef pop_back<s>::type r;

Return type:	Back Extensible Sequence.
Precondition:	`empty<s>::value == false`.
Semantics:	Equivalent to `erase<s,end<s>::type>::type;`.
Postcondition:	`size<r>::value == size<s>::value - 1`.

Complexity

Amortized constant time.

Example

typedef vector<long>::type types1;
typedef vector<long,int>::type types2;
typedef vector<long,int,char>::type types3;

typedef pop_back<types1>::type result1;
typedef pop_back<types2>::type result2;
typedef pop_back<types3>::type result3;
    
BOOST_MPL_ASSERT_RELATION( size<result1>::value, ==, 0 );
BOOST_MPL_ASSERT_RELATION( size<result2>::value, ==, 1 );
BOOST_MPL_ASSERT_RELATION( size<result3>::value, ==, 2 );
    
BOOST_MPL_ASSERT(( is_same< back<result2>::type, long> ));
BOOST_MPL_ASSERT(( is_same< back<result3>::type, int > ));