Boost C++ Libraries

...one of the most highly regarded and expertly designed C++ library projects in the world. — Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

This is an older version of Boost and was released in 2014. The current version is 1.89.0.

key_of

key_of

Description

Returns the key type associated with the element referenced by an associative iterator.

Synopsis

template<
    typename I
    >
struct key_of
{
    typedef unspecified type;
};

Table 1.20. Parameters

Parameter	Requirement	Description
`I`	Model of Associative Iterator	Operation's argument

Expression Semantics

result_of::key_of<I>::type

Return type: Any type

Semantics: Returns the key type associated with the element referenced by an associative iterator I.

Header

#include <boost/fusion/iterator/key_of.hpp>
#include <boost/fusion/include/key_of.hpp>

Example

typedef map<pair<float,int> > vec;
typedef result_of::begin<vec>::type first;

BOOST_MPL_ASSERT((boost::is_same<result_of::key_of<first>::type, float>));