pop_front

Synopsis

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

Description

pop_front performs a removal at the beginning of the sequence with guaranteed O(1) complexity.

Header

#include <boost/mpl/pop_front.hpp>

Model of

Tag Dispatched Metafunction

Parameters

Parameter	Requirement	Description
`Sequence`	Front Extensible Sequence	A sequence to erase the first element from.

Expression semantics

For any Front Extensible Sequence s:

typedef pop_front<s>::type r;

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

Complexity

Amortized constant time.

Example

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

typedef pop_front<types1>::type result1;
typedef pop_front<types2>::type result2;
typedef pop_front<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< front<result2>::type, long > ));
BOOST_MPL_ASSERT(( is_same< front<result3>::type, int > ));