| .. Sequences/Intrinsic Metafunctions//pop_front |
| |
| pop_front |
| ========= |
| |
| Synopsis |
| -------- |
| |
| .. parsed-literal:: |
| |
| 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 |
| ------ |
| |
| .. parsed-literal:: |
| |
| #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``: |
| |
| .. parsed-literal:: |
| |
| 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 |
| ------- |
| |
| .. parsed-literal:: |
| |
| 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 > )); |
| |
| |
| See also |
| -------- |
| |
| |Front Extensible Sequence|, |erase|, |push_front|, |front|, |pop_back| |
| |
| |
| .. 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) |
