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            Returns the result type of at_key[9].
          
template< typename Seq, typename Key> struct at_key { typedef unspecified type; };
Table 1.33. Parameters
| Parameter | Requirement | Description | 
|---|---|---|
| 
                       | A model of Associative Sequence | Argument sequence | 
| 
                       | Any type | Key type | 
result_of::at_key<Seq, Key>::type
Return type: Any type.
            Precondition: has_key<Seq, Key>::type::value == true
            (where Seq is not Unbounded Sequence)
          
            Semantics: Returns the result of using
            at_key to access the element
            with key type Key in
            Seq.
          
#include <boost/fusion/sequence/intrinsic/at_key.hpp> #include <boost/fusion/include/at_key.hpp>
typedefmap<pair<int, char>,pair<char, char>,pair<double, char> > mymap; BOOST_MPL_ASSERT((boost::is_same<result_of::at_key<mymap, int>::type, char&>));
[9] 
              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