| .. .. Algorithms/Iteration Algorithms |
| |
| .. UNFINISHED: Expression semantics and everything that follows |
| |
| |
| iter_fold_if |
| ============ |
| |
| Synopsis |
| -------- |
| |
| .. parsed-literal:: |
| |
| template< |
| typename Sequence |
| , typename State |
| , typename ForwardOp |
| , typename ForwardPred |
| , typename BackwardOp = |unspecified| |
| , typename BackwardPred = |unspecified| |
| > |
| struct iter_fold_if |
| { |
| typedef |unspecified| type; |
| }; |
| |
| |
| Description |
| ----------- |
| |
| Returns the result of the successive application of binary ``ForwardOp`` to the result |
| of the previous ``ForwardOp`` invocation (``State`` if it's the first call) and each |
| iterator in the sequence range determined by ``ForwardPred`` predicate. If ``BackwardOp`` |
| is provided, it's similarly applied on backward traversal to the result of the |
| previous ``BackwardOp`` invocation (the last result returned by ``ForwardOp` if it's |
| the first call) and each iterator in the sequence range determined by |
| ``BackwardPred`` predicate. |
| |
| |
| Header |
| ------ |
| |
| .. parsed-literal:: |
| |
| #include <boost/mpl/iter_fold_if.hpp> |
| |
| |
| Parameters |
| ---------- |
| |
| +-------------------+-------------------------------+-----------------------------------------------+ |
| | Parameter | Requirement | Description | |
| +===============+===================================+===============================================+ |
| | ``Sequence`` | |Forward Sequence| | A sequence to iterate. | |
| +-------------------+-------------------------------+-----------------------------------------------+ |
| | ``State`` | Any type | The initial state for the first ``BackwardOp``| |
| | | | / ``ForwardOp`` application. | |
| +-------------------+-------------------------------+-----------------------------------------------+ |
| | ``ForwardOp`` | Binary |Lambda Expression| | The operation to be executed on forward | |
| | | | traversal. | |
| +-------------------+-------------------------------+-----------------------------------------------+ |
| | ``ForwardPred`` | Binary |Lambda Expression| | The forward traversal predicate. | |
| +-------------------+-------------------------------+-----------------------------------------------+ |
| | ``BackwardOp`` | Binary |Lambda Expression| | The operation to be executed on backward | |
| | | | traversal. | |
| +-------------------+-------------------------------+-----------------------------------------------+ |
| | ``BackwardPred`` | Binary |Lambda Expression| | The backward traversal predicate. | |
| +-------------------+-------------------------------+-----------------------------------------------+ |
| |
| |
| Expression semantics |
| -------------------- |
| |
| For any |Forward Sequence| ``s``, binary |Lambda Expression| ``op``, and an |
| arbitrary type ``state``: |
| |
| |
| .. parsed-literal:: |
| |
| typedef iter_fold<Sequence,T,Op>::type t; |
| |
| :Return type: |
| A type |
| |
| :Semantics: |
| Equivalent to |
| |
| .. parsed-literal:: |
| |
| typedef lambda<Op>::type op; |
| typedef begin<Sequence>::type i1; |
| typedef apply<op,T,i1>::type t1; |
| typedef i1::next i2; |
| typedef apply<op,t1,i2>::type t2; |
| ... |
| typedef apply<op,T,in>::type tn; |
| typedef in::next last; |
| typedef tn t |
| |
| where ``n == size<Sequence>::value`` and ``last`` is identical to ``end<Sequence>::type``; |
| |
| Equivalent to ``typedef T t;`` if the sequence is empty. |
| |
| |
| |
| Complexity |
| ---------- |
| |
| Linear. Exactly ``size<Sequence>::value`` applications of ``ForwardOp``. |
| |
| |
| Example |
| ------- |
| |
| .. parsed-literal:: |
| |
| typedef list_c<int,5,-1,0,7,2,0,-5,4> numbers; |
| typedef iter_fold< |
| numbers |
| , begin<numbers>::type |
| , if_< less< deref<_1>, deref<_2> >,_2,_1 > |
| >::type max_element_iter; |
| |
| BOOST_STATIC_ASSERT(max_element_iter::type::value == 7); |
| |
| |
| |
| See also |
| -------- |
| |
| Algorithms, ``iter_fold_backward``, ``fold``, ``fold_backward``, ``copy``, ``copy_backward`` |
| |
| |
| .. 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) |
