at_key

Description

Returns the result type of at_key^[9].

Synopsis

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

Table 1.33. 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.

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.

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&>));

^[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