Boost
C++ Libraries
...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
Boost
C++ Libraries
...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
| Front Page / Algorithms / Iteration Algorithms / reverse_fold |
template<
typename Sequence
, typename State
, typename BackwardOp
, typename ForwardOp = _1
>
struct reverse_fold
{
typedef unspecified type;
};
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.
#include <boost/mpl/reverse_fold.hpp>
| 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. |
For any Forward Sequence s, binary Lambda Expression backward_op and forward_op, and arbitrary type state:
typedef reverse_fold< s,state,backward_op >::type t;
| Return type: | A type |
|---|---|
| Semantics: | Equivalent to typedef lambda<backward_op>::type op; typedef reverse_iter_fold< s , state , apply_wrap2< op, _1, deref<_2> > >::type t; |
typedef reverse_fold< s,state,backward_op,forward_op >::type t;
| Return type: | A type. |
|---|---|
| Semantics: | Equivalent to typedef reverse_fold< Sequence , fold<s,state,forward_op>::type , backward_op >::type t; |
Linear. Exactly size<s>::value applications of backward_op and forward_op.
Remove non-negative elements from a sequence [2].
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 > ));
| [2] | See remove_if for a more compact way to do this. |