| .. Algorithms/Iteration Algorithms//reverse_fold |
| |
| reverse_fold |
| ============ |
| |
| Synopsis |
| -------- |
| |
| .. parsed-literal:: |
| |
| template< |
| typename Sequence |
| , typename State |
| , typename BackwardOp |
| , typename ForwardOp = _1 |
| > |
| struct reverse_fold |
| { |
| typedef |unspecified| type; |
| }; |
| |
| |
| |
| Description |
| ----------- |
| |
| Returns the result of the successive application of binary ``BackwardOp`` to the |
| result of the previous ``BackwardOp`` invocation (``State`` if it's the first call) |
| and every element in the range [``begin<Sequence>::type``, ``end<Sequence>::type``) in |
| reverse order. If ``ForwardOp`` is provided, then it is applied on forward |
| traversal to form the result that is passed to the first ``BackwardOp`` call. |
| |
| |
| Header |
| ------ |
| |
| .. parsed-literal:: |
| |
| #include <boost/mpl/reverse_fold.hpp> |
| |
| |
| |
| Parameters |
| ---------- |
| |
| Parameters |
| ---------- |
| |
| +---------------+-------------------------------+-----------------------------------------------+ |
| | Parameter | Requirement | Description | |
| +===============+===============================+===============================================+ |
| | ``Sequence`` | |Forward Sequence| | A sequence to iterate. | |
| +---------------+-------------------------------+-----------------------------------------------+ |
| | ``State`` | Any type | The initial state for the first ``BackwardOp``| |
| | | | / ``ForwardOp`` application. | |
| +---------------+-------------------------------+-----------------------------------------------+ |
| | ``BackwardOp``| Binary |Lambda Expression| | The operation to be executed on backward | |
| | | | traversal. | |
| +---------------+-------------------------------+-----------------------------------------------+ |
| | ``ForwardOp`` | Binary |Lambda Expression| | The operation to be executed on forward | |
| | | | traversal. | |
| +---------------+-------------------------------+-----------------------------------------------+ |
| |
| |
| Expression semantics |
| -------------------- |
| |
| For any |Forward Sequence| ``s``, binary |Lambda Expression| ``backward_op`` and ``forward_op``, |
| and arbitrary type ``state``: |
| |
| .. parsed-literal:: |
| |
| typedef reverse_fold< s,state,backward_op >::type t; |
| |
| :Return type: |
| A type |
| |
| :Semantics: |
| Equivalent to |
| |
| .. parsed-literal:: |
| |
| typedef lambda<backward_op>::type op; |
| typedef reverse_iter_fold< |
| s |
| , state |
| , apply_wrap2< op, _1, deref<_2> > |
| >::type t; |
| |
| |
| .. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| |
| |
| .. parsed-literal:: |
| |
| typedef reverse_fold< s,state,backward_op,forward_op >::type t; |
| |
| |
| :Return type: |
| A type. |
| |
| :Semantics: |
| Equivalent to |
| |
| .. parsed-literal:: |
| |
| typedef reverse_fold< |
| Sequence |
| , fold<s,state,forward_op>::type |
| , backward_op |
| >::type t; |
| |
| |
| Complexity |
| ---------- |
| |
| Linear. Exactly ``size<s>::value`` applications of ``backward_op`` and ``forward_op``. |
| |
| |
| Example |
| ------- |
| |
| Remove non-negative elements from a sequence [#reverse_fold_note]_. |
| |
| .. parsed-literal:: |
| |
| typedef list_c<int,5,-1,0,-7,-2,0,-5,4> numbers; |
| typedef list_c<int,-1,-7,-2,-5> negatives; |
| typedef reverse_fold< |
| numbers |
| , list_c<int> |
| , if_< less< _2,int_<0> >, push_front<_1,_2,>, _1 > |
| >::type result; |
| |
| BOOST_MPL_ASSERT(( equal< negatives,result > )); |
| |
| |
| .. [#reverse_fold_note] See ``remove_if`` for a more compact way to do this. |
| |
| |
| See also |
| -------- |
| |
| |Algorithms|, |fold|, |reverse_iter_fold|, |iter_fold| |
| |
| |
| .. 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) |
