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For a given sequence, filter returns a new sequences containing only the elements of a specified type.
template<
    typename T,
    typename Sequence
    >
typename result_of::filter<Sequence const, T>::type filter(Sequence const& seq);
Table 1.66. Parameters
| Parameter | Requirement | Description | 
|---|---|---|
| 
                       | A model of Forward Sequence | Operation's argument | 
| 
                       | Any type | The type to retain | 
filter<T>(seq);
Return type:
seq
                implements the Associative
                Sequence model.
              
            Semantics: Returns a sequence containing
            all the elements of seq
            of type T. Equivalent
            to filter_if<boost::same_type<_, T> >(seq)
Constant. Returns a view which is lazily evaluated.
#include <boost/fusion/algorithm/transformation/filter.hpp> #include <boost/fusion/include/filter.hpp>
constvector<int,int,long,long> vec(1,2,3,4); assert(filter<int>(vec) ==make_vector(1,2));