115 lines
3.1 KiB
ReStructuredText
115 lines
3.1 KiB
ReStructuredText
.. Algorithms/Iteration Algorithms//iter_fold
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iter_fold
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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 State
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, typename ForwardOp
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>
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struct iter_fold
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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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Returns the result of the successive application of binary ``ForwardOp`` to the result
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of the previous ``ForwardOp`` invocation (``State`` if it's the first call) and each
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iterator in the range [``begin<Sequence>::type``, ``end<Sequence>::type``) in order.
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Header
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------
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.. parsed-literal::
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#include <boost/mpl/iter_fold.hpp>
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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`` | |Forward Sequence| | A sequence to iterate. |
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+---------------+-------------------------------+---------------------------------------------------+
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| ``State`` | Any type | The initial state for the first ``ForwardOp`` |
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| | | application. |
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+---------------+-------------------------------+---------------------------------------------------+
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| ``ForwardOp`` | Binary |Lambda Expression| | The operation to be executed on forward |
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| | | traversal. |
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+---------------+-------------------------------+---------------------------------------------------+
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Expression semantics
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--------------------
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For any |Forward Sequence| ``s``, binary |Lambda Expression| ``op``, and an
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arbitrary type ``state``:
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.. parsed-literal::
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typedef iter_fold<s,state,op>::type t;
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:Return type:
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A type.
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:Semantics:
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Equivalent to
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.. parsed-literal::
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typedef begin<Sequence>::type i\ :sub:`1`;
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typedef apply<op,state,i\ :sub:`1`>::type state\ :sub:`1`;
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typedef next<i\ :sub:`1`>::type i\ :sub:`2`;
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typedef apply<op,state\ :sub:`1`,i\ :sub:`2`>::type state\ :sub:`2`;
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|...|
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typedef apply<op,state\ :sub:`n-1`,i\ :sub:`n`>::type state\ :sub:`n`;
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typedef next<i\ :sub:`n`>::type last;
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typedef state\ :sub:`n` t;
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where ``n == size<s>::value`` and ``last`` is identical to ``end<s>::type``; equivalent
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to ``typedef state t;`` if ``empty<s>::value == true``.
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Complexity
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----------
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Linear. Exactly ``size<s>::value`` applications of ``op``.
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Example
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-------
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.. parsed-literal::
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typedef vector_c<int,5,-1,0,7,2,0,-5,4> numbers;
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typedef iter_fold<
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numbers
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, begin<numbers>::type
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, if_< less< deref<_1>, deref<_2> >,_2,_1 >
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>::type max_element_iter;
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BOOST_MPL_ASSERT_RELATION( deref<max_element_iter>::type::value, ==, 7 );
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See also
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--------
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|Algorithms|, |reverse_iter_fold|, |fold|, |reverse_fold|, |copy|
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