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##### at_key

###### Description

Returns the result type of `at_key`[8].

###### Synopsis

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

Table 1.34. Parameters

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

###### Expression Semantics

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

Return type: Any type.

Semantics: Returns the result of using `at_key` to access the element with key type `Key` in `Seq`.

###### Header

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

###### Example

    typedef map<pair<int, char>, pair<char, char>, pair<double, char> > mymap;
    BOOST_MPL_ASSERT((boost::is_same<result_of::at_key<mymap, int>::type, char&>));

[8] `result_of::at_key` reflects the actual return type of the function `at_key`. __sequence__s typically return references to its elements via the `at_key` function. If you want to get the actual element type, use `result_of::value_at_key`