pair

Description

Fusion pair type is a half runtime pair. A half runtime pair is similar to a std::pair, but, unlike std::pair, the first type does not have data. It is used as elements in maps, for example.

Synopsis

template <typename First, typename Second>
struct pair;

namespace result_of
{
    template <typename Pair>
    struct first;

    template <typename Pair>
    struct second;

    template <typename First, typename Second>
    struct make_pair;
}

template <typename First, typename Second>
typename result_of::make_pair<First,Second>::type
make_pair(Second const &);

Template parameters

Parameter	Description
First	The first type. This is purely a type. No data is held.
Second	The second type. This contains data.

Notation

P: Fusion pair type
p, p2: Fusion pairs
F, S: Arbitrary types
s: Value of type S
o: Output stream
i: Input stream

Expression Semantics

Expression	Semantics
`P::first_type`	The type of the first template parameter, `F`, equivalent to `result_of::first<P>::type`.
`P::second_type`	The type of the second template parameter, `S`, equivalent to `result_of::second<P>::type`.
`P()`	Default construction.
`P(s)`	Construct a pair given value for the second type, `s`.
`P(p2)`	Copy constructs a pair from another pair, `p2`.
`p.second`	Get the data from `p1`.
`p = p2`	Assigns a pair, `p1`, from another pair, `p2`.
make_pair<F>(s)	Make a pair given the first type, `F`, and a value for the second type, `s`. The second type assumes the type of `s`
`o << p`	Output `p` to output stream, `o`.
`i >> p`	Input `p` from input stream, `i`.
`p == p2`	Tests two pairs for equality.
`p != p2`	Tests two pairs for inequality.

Header

#include <boost/fusion/support/pair.hpp>
#include <boost/fusion/include/pair.hpp>

Example

pair<int, char> p('X');
std::cout << p << std::endl;
std::cout << make_pair<int>('X') << std::endl;
assert((p == make_pair<int>('X')));