/*!
@file
Forward declares `boost::hana::map`.
@copyright Louis Dionne 2013-2017
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