filter_view

Synopsis

template<
      typename Sequence
    , typename Pred
    >
struct filter_view
{
    // unspecified
    // ...
};

Description

A view into a subset of Sequence's elements satisfying the predicate Pred.

Header

#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
filter_view<s,pred> filter_view<s,pred>::type	A lazy Forward Sequence sequence of all the elements in the range [`begin<s>::type`, `end<s>::type`) that satisfy the predicate `pred`.
`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.

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 > ));