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Front Page / Sequences / Intrinsic Metafunctions / push_front

push_front

Synopsis

template<
      typename Sequence
    , typename T
    >
struct push_front
{
    typedef unspecified type;
};

Description

push_front performs an insertion at the beginning of the sequence with guaranteed O(1) complexity.

Header

#include <boost/mpl/push_front.hpp>

Model of

Tag Dispatched Metafunction

Parameters

Parameter Requirement Description
Sequence Front Extensible Sequence A sequence to insert into.
T Any type The element to be inserted.

Expression semantics

For any Front Extensible Sequence s and arbitrary type x:

typedef push_front<s,x>::type r;
Return type:

Front Extensible Sequence.

Semantics:

Equivalent to

typedef insert< s,begin<s>::type,x >::type r;
Postcondition:

size<r>::value == size<s>::value + 1; front<r>::type is identical to x.

Complexity

Amortized constant time.

Example

typedef vector_c<int,1,2,3,5,8,13,21> v;
BOOST_MPL_ASSERT_RELATION( size<v>::value, ==, 7 );

typedef push_front< v,integral_c<int,1> >::type fibonacci;
BOOST_MPL_ASSERT_RELATION( size<fibonacci>::value, ==, 8 );

BOOST_MPL_ASSERT(( equal<
      fibonacci
    , vector_c<int,1,1,2,3,5,8,13,21>
    , equal_to<_,_>
    > ));

See also

Front Extensible Sequence, insert, pop_front, front, push_back