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//
// immer: immutable data structures for C++
// Copyright (C) 2016, 2017, 2018 Juan Pedro Bolivar Puente
//
// This software is distributed under the Boost Software License, Version 1.0.
// See accompanying file LICENSE or copy at http://boost.org/LICENSE_1_0.txt
//
#pragma once
#include <immer/detail/hamts/champ.hpp>
#include <immer/detail/hamts/champ_iterator.hpp>
#include <immer/memory_policy.hpp>
#include <functional>
namespace immer {
template <typename K,
typename T,
typename Hash,
typename Equal,
typename MemoryPolicy,
detail::hamts::bits_t B>
class map_transient;
/*!
* Immutable unordered mapping of values from type `K` to type `T`.
*
* @tparam K The type of the keys.
* @tparam T The type of the values to be stored in the container.
* @tparam Hash The type of a function object capable of hashing
* values of type `T`.
* @tparam Equal The type of a function object capable of comparing
* values of type `T`.
* @tparam MemoryPolicy Memory management policy. See @ref
* memory_policy.
*
* @rst
*
* This cotainer provides a good trade-off between cache locality,
* search, update performance and structural sharing. It does so by
* storing the data in contiguous chunks of :math:`2^{B}` elements.
* When storing big objects, the size of these contiguous chunks can
* become too big, damaging performance. If this is measured to be
* problematic for a specific use-case, it can be solved by using a
* `immer::box` to wrap the type `T`.
*
* **Example**
* .. literalinclude:: ../example/map/intro.cpp
* :language: c++
* :start-after: intro/start
* :end-before: intro/end
*
* @endrst
*
*/
template <typename K,
typename T,
typename Hash = std::hash<K>,
typename Equal = std::equal_to<K>,
typename MemoryPolicy = default_memory_policy,
detail::hamts::bits_t B = default_bits>
class map
{
using value_t = std::pair<K, T>;
struct project_value
{
const T& operator()(const value_t& v) const noexcept
{
return v.second;
}
};
struct project_value_ptr
{
const T* operator()(const value_t& v) const noexcept
{
return &v.second;
}
};
struct combine_value
{
template <typename Kf, typename Tf>
value_t operator()(Kf&& k, Tf&& v) const
{
return {std::forward<Kf>(k), std::forward<Tf>(v)};
}
};
struct default_value
{
const T& operator()() const
{
static T v{};
return v;
}
};
struct error_value
{
const T& operator()() const
{
throw std::out_of_range{"key not found"};
}
};
struct hash_key
{
auto operator()(const value_t& v) { return Hash{}(v.first); }
auto operator()(const K& v) { return Hash{}(v); }
};
struct equal_key
{
auto operator()(const value_t& a, const value_t& b)
{
return Equal{}(a.first, b.first);
}
auto operator()(const value_t& a, const K& b)
{
return Equal{}(a.first, b);
}
};
struct equal_value
{
auto operator()(const value_t& a, const value_t& b)
{
return Equal{}(a.first, b.first) && a.second == b.second;
}
};
using impl_t =
detail::hamts::champ<value_t, hash_key, equal_key, MemoryPolicy, B>;
public:
using key_type = K;
using mapped_type = T;
using value_type = std::pair<K, T>;
using size_type = detail::hamts::size_t;
using diference_type = std::ptrdiff_t;
using hasher = Hash;
using key_equal = Equal;
using reference = const value_type&;
using const_reference = const value_type&;
using iterator = detail::hamts::
champ_iterator<value_t, hash_key, equal_key, MemoryPolicy, B>;
using const_iterator = iterator;
using transient_type = map_transient<K, T, Hash, Equal, MemoryPolicy, B>;
/*!
* Default constructor. It creates a set of `size() == 0`. It
* does not allocate memory and its complexity is @f$ O(1) @f$.
*/
map() = default;
/*!
* Returns an iterator pointing at the first element of the
* collection. It does not allocate memory and its complexity is
* @f$ O(1) @f$.
*/
IMMER_NODISCARD iterator begin() const { return {impl_}; }
/*!
* Returns an iterator pointing just after the last element of the
* collection. It does not allocate and its complexity is @f$ O(1) @f$.
*/
IMMER_NODISCARD iterator end() const
{
return {impl_, typename iterator::end_t{}};
}
/*!
* Returns the number of elements in the container. It does
* not allocate memory and its complexity is @f$ O(1) @f$.
*/
IMMER_NODISCARD size_type size() const { return impl_.size; }
/*!
* Returns `true` if there are no elements in the container. It
* does not allocate memory and its complexity is @f$ O(1) @f$.
*/
IMMER_NODISCARD bool empty() const { return impl_.size == 0; }
/*!
* Returns `1` when the key `k` is contained in the map or `0`
* otherwise. It won't allocate memory and its complexity is
* *effectively* @f$ O(1) @f$.
*/
IMMER_NODISCARD size_type count(const K& k) const
{
return impl_.template get<detail::constantly<size_type, 1>,
detail::constantly<size_type, 0>>(k);
}
/*!
* Returns a `const` reference to the values associated to the key
* `k`. If the key is not contained in the map, it returns a
* default constructed value. It does not allocate memory and its
* complexity is *effectively* @f$ O(1) @f$.
*/
IMMER_NODISCARD const T& operator[](const K& k) const
{
return impl_.template get<project_value, default_value>(k);
}
/*!
* Returns a `const` reference to the values associated to the key
* `k`. If the key is not contained in the map, throws an
* `std::out_of_range` error. It does not allocate memory and its
* complexity is *effectively* @f$ O(1) @f$.
*/
const T& at(const K& k) const
{
return impl_.template get<project_value, error_value>(k);
}
/*!
* Returns a pointer to the value associated with the key `k`. If
* the key is not contained in the map, a `nullptr` is returned.
* It does not allocate memory and its complexity is *effectively*
* @f$ O(1) @f$.
*
* @rst
*
* .. admonition:: Why doesn't this function return an iterator?
*
* Associative containers from the C++ standard library provide a
* ``find`` method that returns an iterator pointing to the
* element in the container or ``end()`` when the key is missing.
* In the case of an unordered container, the only meaningful
* thing one may do with it is to compare it with the end, to
* test if the find was succesfull, and dereference it. This
* comparison is cumbersome compared to testing for a non-empty
* optional value. Furthermore, for an immutable container,
* returning an iterator would have some additional performance
* cost, with no benefits otherwise.
*
* In our opinion, this function should return a
* ``std::optional<const T&>`` but this construction is not valid
* in any current standard. As a compromise we return a
* pointer, which has similar syntactic properties yet it is
* unfortunatelly unnecessarily unrestricted.
*
* @endrst
*/
IMMER_NODISCARD const T* find(const K& k) const
{
return impl_.template get<project_value_ptr,
detail::constantly<const T*, nullptr>>(k);
}
/*!
* Returns whether the sets are equal.
*/
IMMER_NODISCARD bool operator==(const map& other) const
{
return impl_.template equals<equal_value>(other.impl_);
}
IMMER_NODISCARD bool operator!=(const map& other) const
{
return !(*this == other);
}
/*!
* Returns a map containing the association `value`. If the key is
* already in the map, it replaces its association in the map.
* It may allocate memory and its complexity is *effectively* @f$
* O(1) @f$.
*/
IMMER_NODISCARD map insert(value_type value) const
{
return impl_.add(std::move(value));
}
/*!
* Returns a map containing the association `(k, v)`. If the key
* is already in the map, it replaces its association in the map.
* It may allocate memory and its complexity is *effectively* @f$
* O(1) @f$.
*/
IMMER_NODISCARD map set(key_type k, mapped_type v) const
{
return impl_.add({std::move(k), std::move(v)});
}
/*!
* Returns a map replacing the association `(k, v)` by the
* association new association `(k, fn(v))`, where `v` is the
* currently associated value for `k` in the map or a default
* constructed value otherwise. It may allocate memory
* and its complexity is *effectively* @f$ O(1) @f$.
*/
template <typename Fn>
IMMER_NODISCARD map update(key_type k, Fn&& fn) const
{
return impl_
.template update<project_value, default_value, combine_value>(
std::move(k), std::forward<Fn>(fn));
}
/*!
* Returns a map without the key `k`. If the key is not
* associated in the map it returns the same map. It may allocate
* memory and its complexity is *effectively* @f$ O(1) @f$.
*/
IMMER_NODISCARD map erase(const K& k) const { return impl_.sub(k); }
/*!
* Returns an @a transient form of this container, a
* `immer::map_transient`.
*/
IMMER_NODISCARD transient_type transient() const&
{
return transient_type{impl_};
}
IMMER_NODISCARD transient_type transient() &&
{
return transient_type{std::move(impl_)};
}
// Semi-private
const impl_t& impl() const { return impl_; }
private:
friend transient_type;
map(impl_t impl)
: impl_(std::move(impl))
{}
impl_t impl_ = impl_t::empty();
};
} // namespace immer