111 lines
2.2 KiB
ReStructuredText
111 lines
2.2 KiB
ReStructuredText
.. Sequences/Intrinsic Metafunctions//push_front
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push_front
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==========
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Synopsis
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--------
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.. parsed-literal::
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template<
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typename Sequence
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, typename T
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>
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struct push_front
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{
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typedef |unspecified| type;
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};
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Description
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-----------
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``push_front`` performs an insertion at the beginning of the sequence with guaranteed |O(1)|
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complexity.
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Header
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------
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.. parsed-literal::
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#include <boost/mpl/push_front.hpp>
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Model of
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--------
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|Tag Dispatched Metafunction|
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Parameters
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----------
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+---------------+-------------------------------+-----------------------------------------------+
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| Parameter | Requirement | Description |
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+===============+===============================+===============================================+
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| ``Sequence`` | |Front Extensible Sequence| | A sequence to insert into. |
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+---------------+-------------------------------+-----------------------------------------------+
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| ``T`` | Any type | The element to be inserted. |
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+---------------+-------------------------------+-----------------------------------------------+
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Expression semantics
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--------------------
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For any |Front Extensible Sequence| ``s`` and arbitrary type ``x``:
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.. parsed-literal::
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typedef push_front<s,x>::type r;
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:Return type:
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|Front Extensible Sequence|.
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:Semantics:
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Equivalent to
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.. parsed-literal::
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typedef insert< s,begin<s>::type,x >::type r;
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:Postcondition:
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``size<r>::value == size<s>::value + 1``;
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``front<r>::type`` is identical to ``x``.
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Complexity
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----------
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Amortized constant time.
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Example
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-------
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.. parsed-literal::
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typedef vector_c<int,1,2,3,5,8,13,21> v;
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BOOST_MPL_ASSERT_RELATION( size<v>::value, ==, 7 );
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typedef push_front< v,integral_c<int,1> >::type fibonacci;
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BOOST_MPL_ASSERT_RELATION( size<fibonacci>::value, ==, 8 );
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BOOST_MPL_ASSERT(( equal<
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fibonacci
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, vector_c<int,1,1,2,3,5,8,13,21>
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, equal_to<_,_>
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> ));
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See also
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--------
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|Front Extensible Sequence|, |insert|, |pop_front|, |front|, |push_back|
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