filter_if

Description

For a given sequence, filter_if returns a new sequences containing only the elements with types for which a given MPL Lambda Expression evaluates to boost::mpl::true_.

Synopsis

template<
    typename Pred,
    typename Sequence
    >
typename result_of::filter_if<Sequence const, Pred>::type filter_if(Sequence const& seq);

Table 1.65. Parameters

Parameter	Requirement	Description
`seq`	A model of Forward Sequence	Operation's argument
`Pred`	A unary MPL Lambda Expression	The predicate to filter by

Expression Semantics

filter_if<Pred>(seq);

Return type:

A model of Forward Sequence.
A model of Associative Sequence if seq implements the Associative Sequence model.

Semantics: Returns a sequence containing all the elements of seq with types for which Pred evaluates to boost::mpl::true_. The order of the retained elements is the same as in the original sequence.

Complexity

Constant. Returns a view which is lazily evaluated.

Header

#include <boost/fusion/algorithm/transformation/filter_if.hpp>
#include <boost/fusion/include/filter_if.hpp>

Example

const vector<int,int,double,double> vec(1,2,3.0,4.0);
assert(filter_if<is_integral<mpl::_> >(vec) == make_vector(1,2));