#ifndef METAL_MAP_INSERT_KEY_HPP
#define METAL_MAP_INSERT_KEY_HPP

#include "../config.hpp"
#include "../list/append.hpp"
#include "../map/has_key.hpp"
#include "../number/if.hpp"
#include "../pair/pair.hpp"

namespace metal {
/// \ingroup map
///
/// ### Description
/// Inserts a new entry in a \map.
///
/// ### Usage
/// For any \map `m` and \values `k` and `v`
/// \code
///     using result = metal::erase_key<m, k, v>;
/// \endcode
///
/// \pre: `k` is not contained in `metal::keys<m>`
/// \returns: \map
/// \semantics:
///     If `m` associates keys `k_1, ..., k_n` to values `v_1, ..., v_n`,
///     then
///     \code
///         using result = metal::map<
///             metal::pair<k_1, v_1>,
///             ...,
///             metal::pair<k_n, v_n>,
///             metal::pair<k, v>
///         >;
///     \endcode
///
/// ### Example
/// \snippet map.cpp insert_key
///
/// ### See Also
/// \see map, has_key, at_key, erase_key
template <class seq, class key, class val>
using insert_key = metal::if_<
    metal::not_<metal::has_key<seq, key>>,
    metal::append<seq, metal::pair<key, val>>>;
}

#endif