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            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_.
          
template<
    typename Pred,
    typename Sequence
    >
typename result_of::filter_if<Sequence const, Pred>::type filter_if(Sequence const& seq);
Table 1.67. Parameters
| Parameter | Requirement | Description | 
|---|---|---|
| 
                       | A model of Forward Sequence | Operation's argument | 
| 
                       | A unary MPL Lambda Expression | The predicate to filter by | 
filter_if<Pred>(seq);
Return type:
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.
          
Constant. Returns a view which is lazily evaluated.
#include <boost/fusion/algorithm/transformation/filter_if.hpp> #include <boost/fusion/include/filter_if.hpp>
constvector<int,int,double,double> vec(1,2,3.0,4.0); assert(filter_if<is_integral<mpl::_> >(vec) ==make_vector(1,2));