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 /*!
 @file
 Forward declares `boost::hana::map`.
 
 Copyright Louis Dionne 2013-2022
 Distributed under the Boost Software License, Version 1.0.
 (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
  */
 
 #ifndef BOOST_HANA_FWD_MAP_HPP
 #define BOOST_HANA_FWD_MAP_HPP
 
 #include <boost/hana/config.hpp>
 #include <boost/hana/fwd/core/to.hpp>
 #include <boost/hana/fwd/core/make.hpp>
 #include <boost/hana/fwd/erase_key.hpp>
 #include <boost/hana/fwd/insert.hpp>
 #include <boost/hana/fwd/keys.hpp>
 
 
 namespace boost { namespace hana {
     //! Tag representing `hana::map`s.
     //! @relates hana::map
     struct map_tag { };
 
     namespace detail {
         template <typename ...Pairs>
         struct make_map_type;
     }
 
     //! @ingroup group-datatypes
     //! Basic associative container requiring unique, `Comparable` and
     //! `Hashable` keys.
     //!
     //! The order of the elements of the map is unspecified. Also, all the
     //! keys must be `Hashable`, and any two keys with equal hashes must be
     //! `Comparable` with each other at compile-time.
     //!
     //! @note
     //! The actual representation of a `hana::map` is an implementation
     //! detail. As such, one should not assume anything more than what is
     //! explicitly documented as being part of the interface of a map,
     //! such as:
     //! - the presence of additional constructors
     //! - the presence of additional assignment operators
     //! - the fact that `hana::map<Pairs...>` is, or is not, a dependent type
     //! .
     //! In particular, the last point is very important; `hana::map<Pairs...>`
     //! is basically equivalent to
     //! @code
     //!     decltype(hana::make_pair(std::declval<Pairs>()...))
     //! @endcode
     //! which is not something that can be pattern-matched on during template
     //! argument deduction, for example. More details [in the tutorial]
     //! (@ref tutorial-containers-types).
     //!
     //!
     //! Modeled concepts
     //! ----------------
     //! 1. `Comparable`\n
     //! Two maps are equal iff all their keys are equal and are associated
     //! to equal values.
     //! @include example/map/comparable.cpp
     //!
     //! 2. `Searchable`\n
     //! A map can be searched by its keys with a predicate yielding a
     //! compile-time `Logical`. Also note that `operator[]` can be used
     //! instead of `at_key`.
     //! @include example/map/searchable.cpp
     //!
     //! 3. `Foldable`\n
     //! Folding a map is equivalent to folding a list of the key/value pairs
     //! it contains. In particular, since that list is not guaranteed to be
     //! in any specific order, folding a map with an operation that is not
     //! both commutative and associative will yield non-deterministic behavior.
     //! @include example/map/foldable.cpp
     //!
     //!
     //! Conversion from any `Foldable`
     //! ------------------------------
     //! Any `Foldable` of `Product`s can be converted to a `hana::map` with
     //! `hana::to<hana::map_tag>` or, equivalently, `hana::to_map`. If the
     //! `Foldable` contains duplicate keys, only the value associated to the
     //! first occurence of each key is kept.
     //! @include example/map/to.cpp
     //!
     //!
     //! Example
     //! -------
     //! @include example/map/map.cpp
 #ifdef BOOST_HANA_DOXYGEN_INVOKED
     template <typename ...Pairs>
     struct map {
         //! Default-construct a map. This constructor only exists when all the
         //! elements of the map are default-constructible.
         constexpr map() = default;
 
         //! Copy-construct a map from another map. This constructor only
         //! exists when all the elements of the map are copy-constructible.
         constexpr map(map const& other) = default;
 
         //! Move-construct a map from another map. This constructor only
         //! exists when all the elements of the map are move-constructible.
         constexpr map(map&& other) = default;
 
         //! Construct the map from the provided pairs. `P...` must be pairs of
         //! the same type (modulo ref and cv-qualifiers), and in the same order,
         //! as those appearing in `Pairs...`. The pairs provided to this
         //! constructor are emplaced into the map's storage using perfect
         //! forwarding.
         template <typename ...P>
         explicit constexpr map(P&& ...pairs);
 
         //! Assign a map to another map __with the exact same type__. Only
         //! exists when all the elements of the map are copy-assignable.
         constexpr map& operator=(map const& other);
 
         //! Move-assign a map to another map __with the exact same type__.
         //! Only exists when all the elements of the map are move-assignable.
         constexpr map& operator=(map&& other);
 
         //! Equivalent to `hana::equal`
         template <typename X, typename Y>
         friend constexpr auto operator==(X&& x, Y&& y);
 
         //! Equivalent to `hana::not_equal`
         template <typename X, typename Y>
         friend constexpr auto operator!=(X&& x, Y&& y);
 
         //! Equivalent to `hana::at_key`
         template <typename Key>
         constexpr decltype(auto) operator[](Key&& key);
     };
 #else
     template <typename ...Pairs>
     using map = typename detail::make_map_type<Pairs...>::type;
 #endif
 
     //! Function object for creating a `hana::map`.
     //! @relates hana::map
     //!
     //! Given zero or more `Product`s representing key/value associations,
     //! `make<map_tag>` returns a `hana::map` associating these keys to these
     //! values.
     //!
     //! `make<map_tag>` requires all the keys to be unique and to have
     //! different hashes. If you need to create a map with duplicate keys
     //! or with keys whose hashes might collide, use `hana::to_map` or
     //! insert `(key, value)` pairs to an empty map successively. However,
     //! be aware that doing so will be much more compile-time intensive than
     //! using `make<map_tag>`, because the uniqueness of keys will have to be
     //! enforced.
     //!
     //!
     //! Example
     //! -------
     //! @include example/map/make.cpp
 #ifdef BOOST_HANA_DOXYGEN_INVOKED
     template <>
     constexpr auto make<map_tag> = [](auto&& ...pairs) {
         return map<implementation_defined>{forwarded(pairs)...};
     };
 #endif
 
     //! Alias to `make<map_tag>`; provided for convenience.
     //! @relates hana::map
     //!
     //!
     //! Example
     //! -------
     //! @include example/map/make.cpp
     BOOST_HANA_INLINE_VARIABLE constexpr auto make_map = make<map_tag>;
 
     //! Equivalent to `to<map_tag>`; provided for convenience.
     //! @relates hana::map
     BOOST_HANA_INLINE_VARIABLE constexpr auto to_map = to<map_tag>;
 
     //! Returns a `Sequence` of the keys of the map, in unspecified order.
     //! @relates hana::map
     //!
     //!
     //! Example
     //! -------
     //! @include example/map/keys.cpp
 #ifdef BOOST_HANA_DOXYGEN_INVOKED
     constexpr auto keys = [](auto&& map) {
         return implementation_defined;
     };
 #endif
 
     //! Returns a `Sequence` of the values of the map, in unspecified order.
     //! @relates hana::map
     //!
     //!
     //! Example
     //! -------
     //! @include example/map/values.cpp
 #ifdef BOOST_HANA_DOXYGEN_INVOKED
     constexpr auto values = [](auto&& map) -> decltype(auto) {
         return implementation_defined;
     };
 #else
     struct values_t {
         template <typename Map>
         constexpr decltype(auto) operator()(Map&& map) const;
     };
 
     BOOST_HANA_INLINE_VARIABLE constexpr values_t values{};
 #endif
 
     //! Inserts a new key/value pair in a map.
     //! @relates hana::map
     //!
     //! Given a `(key, value)` pair, `insert` inserts this new pair into a
     //! map. If the map already contains this key, nothing is done and the
     //! map is returned as-is.
     //!
     //!
     //! @param map
     //! The map in which to insert a `(key,value)` pair.
     //!
     //! @param pair
     //! An arbitrary `Product` representing a `(key, value)` pair to insert
     //! in the map. The `key` must be compile-time `Comparable`.
     //!
     //!
     //! Example
     //! -------
     //! @include example/map/insert.cpp
 #ifdef BOOST_HANA_DOXYGEN_INVOKED
     constexpr auto insert = [](auto&& map, auto&& pair) {
         return tag-dispatched;
     };
 #endif
 
     //! Removes a key/value pair from a map.
     //! @relates hana::map
     //!
     //! Returns a new `hana::map` containing all the elements of the original,
     //! except for the `(key, value)` pair whose `key` compares `equal`
     //! to the given key. If the map does not contain such an element,
     //! a new map equal to the original is returned.
     //!
     //!
     //! @param map
     //! The map in which to erase a `key`.
     //!
     //! @param key
     //! A key to remove from the map. It must be compile-time `Comparable`.
     //!
     //!
     //! Example
     //! -------
     //! @include example/map/erase_key.cpp
 #ifdef BOOST_HANA_DOXYGEN_INVOKED
     constexpr auto erase_key = [](auto&& map, auto&& key) {
         return tag-dispatched;
     };
 #endif
 
     //! Returns the union of two maps.
     //! @relates hana::map
     //!
     //! Given two maps `xs` and `ys`, `hana::union_(xs, ys)` is a new map
     //! containing all the elements of `xs` and all the elements of `ys`,
     //! without duplicates. If both `xs` and `ys` contain an element with the
     //! same `key`, the one in `ys` is taken. Functionally,
     //! `hana::union_(xs, ys)` is equivalent to
     //! @code
     //! hana::fold_left(xs, ys, hana::insert)
     //! @endcode
     //!
     //! @param xs, ys
     //! The two maps to compute the union of.
     //!
     //!
     //! Example
     //! -------
     //! @include example/map/union.cpp
 #ifdef BOOST_HANA_DOXYGEN_INVOKED
     constexpr auto union_ = [](auto&& xs, auto&& ys) {
         return tag-dispatched;
     };
 #endif
 
     //! Returns the intersection of two maps.
     //! @relates hana::map
     //!
     //! Given two maps `xs` and `ys`, `intersection(xs, ys)` is a new map
     //! containing exactly those (key, value) pairs from xs, for which key
     //! is present in `ys`.
     //! In other words, the following holds for any object `pair(k, v)`:
     //! @code
     //!     pair(k, v) ^in^ intersection(xs, ys) if and only if (k, v) ^in^ xs && k ^in^ keys(ys)
     //! @endcode
     //!
     //!
     //! @note
     //! This function is not commutative, i.e. `intersection(xs, ys)` is not
     //! necessarily the same as `intersection(ys, xs)`. Indeed, the set of keys
     //! in `intersection(xs, ys)` is always the same as the set of keys in
     //! `intersection(ys, xs)`, but the value associated to each key may be
     //! different. `intersection(xs, ys)` contains values present in `xs`, and
     //! `intersection(ys, xs)` contains values present in `ys`.
     //!
     //!
     //! @param xs, ys
     //! Two maps to intersect.
     //!
     //!
     //! Example
     //! -------
     //! @include example/map/intersection.cpp
 #ifdef BOOST_HANA_DOXYGEN_INVOKED
     constexpr auto intersection = [](auto&& xs, auto&& ys) {
         return tag-dispatched;
     };
 #endif
 
     //! Returns the difference of two maps.
     //! @relates hana::map
     //!
     //! Given two maps `xs` and `ys`, `difference(xs, ys)` is a new map
     //! containing exactly those (key, value) pairs from xs, for which key
     //! is not present in `keys(ys)`.
     //! In other words, the following holds for any object `pair(k, v)`:
     //! @code
     //!     pair(k, v) ^in^ difference(xs, ys) if and only if (k, v) ^in^ xs && k ^not in^ keys(ys)
     //! @endcode
     //!
     //!
     //! @note
     //! This function is not commutative, i.e. `difference(xs, ys)` is not
     //! necessarily the same as `difference(ys, xs)`.
     //! Indeed, consider the case where `xs` is empty and `ys` isn't.
     //! In that case, `difference(xs, ys)` is empty, but `difference(ys, xs)`
     //! is equal to `ys`.
     //! For symmetric version of this operation, see `symmetric_difference`.
     //!
     //!
     //! @param xs, ys
     //! Two maps to compute the difference of.
     //!
     //!
     //! Example
     //! -------
     //! @include example/map/intersection.cpp
 #ifdef BOOST_HANA_DOXYGEN_INVOKED
     constexpr auto difference = [](auto&& xs, auto&& ys) {
         return tag-dispatched;
     };
 #endif
 
     //! Returns the symmetric set-theoretic difference of two maps.
     //! @relates hana::map
     //!
     //! Given two sets `xs` and `ys`, `symmetric_difference(xs, ys)` is a new
     //! map containing all the elements of `xs` whose keys are not contained in `keys(ys)`,
     //! and all the elements of `ys` whose keys are not contained in `keys(xs)`. The
     //! symmetric difference of two maps satisfies the following:
     //! @code
     //!     symmetric_difference(xs, ys) == union_(difference(xs, ys), difference(ys, xs))
     //! @endcode
     //!
     //!
     //! @param xs, ys
     //! Two maps to compute the symmetric difference of.
     //!
     //!
     //! Example
     //! -------
     //! @include example/map/symmetric_difference.cpp
 #ifdef BOOST_HANA_DOXYGEN_INVOKED
 constexpr auto symmetric_difference = [](auto&& xs, auto&& ys) {
         return tag-dispatched;
     };
 #endif
 
 
 }} // end namespace boost::hana
 
 #endif // !BOOST_HANA_FWD_MAP_HPP

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