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##### has_key

###### Description

Returns the result type of `has_key`.

###### Synopsis

    template<
        typename Seq,
        typename Key>
    struct has_key
    {
        typedef unspecified type;
    };

Table 1.33. Parameters

Parameter | Requirement | Description
--- | --- | ---
`Seq` | A model of Forward Sequence | Argument sequence
`Key` | Any type | Key type

###### Expression Semantics

    result_of::has_key<Seq, Key>::type

Return type: An MPL Integral Constant.

Semantics: Returns `mpl::true_` if `Seq` contains an element with key type `Key`, returns `mpl::false_` otherwise.

###### Header

    #include <boost/fusion/sequence/intrinsic/has_key.hpp>
    #include <boost/fusion/include/has_key.hpp>

###### Example

    typedef map<pair<int, char>, pair<char, char>, pair<double, char> > mymap;
    BOOST_MPL_ASSERT((result_of::has_key<mymap, int>));
    BOOST_MPL_ASSERT_NOT((result_of::has_key<mymap, void*>));