filter_view

Description

filter_view is a view into a subset of its underlying sequence's elements satisfying a given predicate (an MPL metafunction). The filter_view presents only those elements for which its predicate evaluates to mpl::true_.

Header

#include <boost/fusion/view/filter_view.hpp>
#include <boost/fusion/include/filter_view.hpp>

Synopsis

template <typename Sequence, typename Pred>
struct filter_view;

Template parameters

Parameter	Description	Default
`Sequence`	A Forward Sequence
`Pred`	Unary Metafunction returning an `mpl::bool_`

Model of

Forward Sequence

Notation

F: A filter_view type
f, f2: Instances of filter_view
s: A Forward Sequence

Expression Semantics

Semantics of an expression is defined only where it differs from, or is not defined in Forward Sequence.

Expression	Semantics
`F(s)`	Creates a `filter_view` given a sequence, `s`.
`F(f)`	Copy constructs a `filter_view` from another `filter_view`, `f`.
`f = f2`	Assigns to a `filter_view`, `f`, from another `filter_view`, `f2`.

Example

using boost::mpl::_;
using boost::mpl::not_;
using boost::is_class;

typedef vector<std::string, char, long, bool, double> vector_type;

vector_type v("a-string", '@', 987654, true, 6.6);
filter_view<vector_type const, not_<is_class<_> > > view(v);
std::cout << view << std::endl;