| .. Sequences/Views//filter_view |
| |
| filter_view |
| =========== |
| |
| Synopsis |
| -------- |
| |
| .. parsed-literal:: |
| |
| template< |
| typename Sequence |
| , typename Pred |
| > |
| struct filter_view |
| { |
| // |unspecified| |
| // |...| |
| }; |
| |
| |
| |
| Description |
| ----------- |
| |
| A view into a subset of ``Sequence``\ 's elements satisfying the predicate ``Pred``. |
| |
| |
| Header |
| ------ |
| |
| .. parsed-literal:: |
| |
| #include <boost/mpl/filter_view.hpp> |
| |
| |
| Model of |
| -------- |
| |
| * |Forward Sequence| |
| |
| |
| Parameters |
| ---------- |
| |
| +---------------+-----------------------------------+-----------------------------------------------+ |
| | Parameter | Requirement | Description | |
| +===============+===================================+===============================================+ |
| | ``Sequence`` | |Forward Sequence| | A sequence to wrap. | |
| +---------------+-----------------------------------+-----------------------------------------------+ |
| | ``Pred`` | Unary |Lambda Expression| | A filtering predicate. | |
| +---------------+-----------------------------------+-----------------------------------------------+ |
| |
| |
| Expression semantics |
| -------------------- |
| |
| Semantics of an expression is defined only where it differs from, or is not |
| defined in |Forward Sequence|. |
| |
| In the following table, ``v`` is an instance of ``filter_view``, ``s`` is an arbitrary |
| |Forward Sequence|, ``pred`` is an unary |Lambda Expression|. |
| |
| +---------------------------------------+-----------------------------------------------------------+ |
| | Expression | Semantics | |
| +=======================================+===========================================================+ |
| | .. parsed-literal:: | A lazy |Forward Sequence| sequence of all the elements in | |
| | | the range |begin/end<s>| that satisfy the predicate | |
| | filter_view<s,pred> | ``pred``. | |
| | filter_view<s,pred>::type | | |
| +---------------------------------------+-----------------------------------------------------------+ |
| | ``size<v>::type`` | The size of ``v``; | |
| | | ``size<v>::value == count_if<s,pred>::value``; | |
| | | linear complexity; see |Forward Sequence|. | |
| +---------------------------------------+-----------------------------------------------------------+ |
| |
| |
| Example |
| ------- |
| |
| Find the largest floating type in a sequence. |
| |
| .. parsed-literal:: |
| |
| typedef vector<int,float,long,float,char[50],long double,char> types; |
| typedef max_element< |
| transform_view< filter_view< types,boost::is_float<_> >, size_of<_> > |
| >::type iter; |
| |
| BOOST_MPL_ASSERT(( is_same< deref<iter::base>::type, long double > )); |
| |
| |
| See also |
| -------- |
| |
| |Sequences|, |Views|, |transform_view|, |joint_view|, |zip_view|, |iterator_range| |
| |
| |
| .. 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) |
