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### is_view

##### Description

Metafunction that evaluates to `mpl::true_` if a certain type `T` is a conforming Fusion View, `mpl::false_` otherwise. A view is a specialized sequence that does not actually contain data. Views hold sequences which may be other views. In general, views are held by other views by value, while non-views are held by other views by reference. `is_view` may be specialized to accommodate clients providing Fusion conforming views.

##### Synopsis

    namespace traits
    {
        template <typename T>
        struct is_view
        {
            typedef unspecified type;
        };
    }

##### Parameters

Parameter | Requirement | Description
--- | --- | ---
`T` | Any type | The type to query.

##### Expression Semantics

    typedef traits::is_view<T>::type c;

Return type: An MPL Boolean Constant.

Semantics: Metafunction that evaluates to `mpl::true_` if a certain type `T` is a conforming Fusion view, `mpl::false_` otherwise.

##### Header

    #include <boost/fusion/support/is_view.hpp>
    #include <boost/fusion/include/is_view.hpp>

##### Example

    BOOST_MPL_ASSERT_NOT(( traits::is_view<std::vector<int> > ));
    BOOST_MPL_ASSERT_NOT(( traits::is_view<int> ));

    using boost::mpl::_
    using boost::is_pointer;
    typedef vector<int*, char, long*, bool, double> vector_type;
    typedef filter_view<vector_type, is_pointer<_> > filter_view_type;
    BOOST_MPL_ASSERT(( traits::is_view<filter_view_type> ));