has_key

Returns a type convertible to bool that evaluates to true if the sequence contains an element associated with a Key, else, evaluates to false.

template <typename Key, typename Sequence>
typename result_of::has_key<Sequence, Key>::type
has_key(Sequence const& seq);

Parameter	Requirement	Description
`seq`	Model of Associative Sequence	The sequence we wish to investigate.
`Key`	Any type	The queried key.

has_key<Key>(seq);

Return type: Convertible to bool.

Semantics: Evaluates to true if the sequence contains an element associated with Key, else, evaluates to false.

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

set<int, char, bool> s(1, 'x', true);
assert(has_key<char>(s) == true);