Pair

as_pair

template<class val >

using metal::as_pair = typedef metal::apply<metal::lambda<metal::pair>, metal::as_list<val> >

#include <metal/pair/pair.hpp>

Description

Constructs a Pair out of any Value that is a specialization of a template class or union that takes exactly two template parameters that are themselves Values.

Usage

For any Value val

using result = metal::as_pair<val>;

Returns

: Pair

Example

IS_SAME(metal::as_pair<std::pair<int, char>>, metal::list<int, char>);
 
IS_SAME(
    metal::as_pair<std::unique_ptr<int>>,
    metal::pair<int, std::default_delete<int>>
);

See Also

See also

pair

first

template<class seq >

using metal::first = typedef metal::if_<metal::is_pair<seq>, metal::front<seq> >

#include <metal/pair/first.hpp>

Description

Retrieves the first element of a Pair.

Usage

For any Pair p

using result = metal::first<p>;

Returns

: Value

Semantics:

If p contains Values p_0 and p_1 in that order, then

using result = p_0;

Example

IS_SAME(metal::first<metal::pair<void, void*>>, void);

See Also

See also

pair, second

is_pair

template<class val >

using metal::is_pair = typedef typename detail::_is_pair<val>::type

#include <metal/pair/pair.hpp>

Description

Checks whether some Value is a Pair.

Usage

For any Value val

using result = metal::is_pair<val>;

Returns

: Number

Semantics:

If val is a Pair, then

using result = metal::true_;

otherwise

using result = metal::false_;

Example

IS_SAME(metal::is_pair<std::pair<int, unsigned>>, metal::false_);
IS_SAME(metal::is_pair<metal::pair<int, unsigned>>, metal::true_);
IS_SAME(metal::is_pair<metal::list<void, void*>>, metal::true_);
IS_SAME(metal::is_pair<metal::list<void>>, metal::false_);

See Also

See also

pair, is_value, is_number, is_lambda, is_list, is_map

pair

template<class x , class y >

using metal::pair = typedef metal::list<x, y>

#include <metal/pair/pair.hpp>

Description

Constructs a Pair out of a pair of Values.

Usage

For any pair of Values x and y

using result = metal::pair<x, y>;

Returns

: Pair

See Also

See also

is_pair

second

template<class seq >

using metal::second = typedef metal::if_<metal::is_pair<seq>, metal::back<seq> >

#include <metal/pair/second.hpp>

Description

Retrieves the second element of a Pair.

Usage

For any Pair p

using result = metal::second<p>;

Returns

: Value

Semantics:

If p contains Values p_0 and p_1 in that order, then

using result = p_1;

Example

IS_SAME(metal::second<metal::pair<void, void*>>, void*);

See Also

See also

pair, first