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* Add key_compare member to ordered_map * Replace == with key_compare in ordered_map * Expose the actual comparison function used by object_t nlohmann::ordered_map uses a different comparison function than the one provided via template parameter. * Introduce a type trait to detect if object_t has a key_compare member. * Rename object_comparator_t to default_object_comparator_t. * Add object_comparator_t to be conditionally defined as object_t::key_compare, if available, or default_object_comparator_t otherwise. * Update the documentation accordingly. Co-authored-by: Niels Lohmann <niels.lohmann@gmail.com> * Add type traits to check if a type is usable as object key Add type trait to check: * if a type is a specialization of a template. * if a type is a json_pointer. * if a type is a basic_json::{const_,}iterator. * if two types are comparable using a given comparison functor. * if a type is comparable to basic_json::object_t::key_type. * if a type has a member type is_transparent. * if a type is usable as object key. * if a type has an erase() function accepting a given KeyType. Co-authored-by: Niels Lohmann <niels.lohmann@gmail.com> * Rework basic_json element access to accept more key types Rework basic_json element access member functions and operators to accept any type that meets the requirements defined by type trait detail::is_usable_as_key_type. Member functions and operators: * at() * operator[] * value() * erase() * find() * count() * contains() Update documentation to reflect these changes. Add unit tests to excercise the new functions using std::string_view. Co-authored-by: Niels Lohmann <niels.lohmann@gmail.com> Co-authored-by: Niels Lohmann <niels.lohmann@gmail.com>
239 lines
7.3 KiB
C++
239 lines
7.3 KiB
C++
#pragma once
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#include <functional> // equal_to, less
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#include <initializer_list> // initializer_list
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#include <iterator> // input_iterator_tag, iterator_traits
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#include <memory> // allocator
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#include <stdexcept> // for out_of_range
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#include <type_traits> // enable_if, is_convertible
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#include <utility> // pair
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#include <vector> // vector
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#include <nlohmann/detail/macro_scope.hpp>
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namespace nlohmann
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{
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/// ordered_map: a minimal map-like container that preserves insertion order
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/// for use within nlohmann::basic_json<ordered_map>
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template <class Key, class T, class IgnoredLess = std::less<Key>,
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class Allocator = std::allocator<std::pair<const Key, T>>>
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struct ordered_map : std::vector<std::pair<const Key, T>, Allocator>
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{
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using key_type = Key;
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using mapped_type = T;
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using Container = std::vector<std::pair<const Key, T>, Allocator>;
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using iterator = typename Container::iterator;
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using const_iterator = typename Container::const_iterator;
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using size_type = typename Container::size_type;
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using value_type = typename Container::value_type;
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#ifdef JSON_HAS_CPP_14
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using key_compare = std::equal_to<>;
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#else
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using key_compare = std::equal_to<Key>;
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#endif
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// Explicit constructors instead of `using Container::Container`
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// otherwise older compilers choke on it (GCC <= 5.5, xcode <= 9.4)
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ordered_map() noexcept(noexcept(Container())) : Container{} {}
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explicit ordered_map(const Allocator& alloc) noexcept(noexcept(Container(alloc))) : Container{alloc} {}
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template <class It>
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ordered_map(It first, It last, const Allocator& alloc = Allocator())
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: Container{first, last, alloc} {}
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ordered_map(std::initializer_list<value_type> init, const Allocator& alloc = Allocator() )
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: Container{init, alloc} {}
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std::pair<iterator, bool> emplace(const key_type& key, T&& t)
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{
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for (auto it = this->begin(); it != this->end(); ++it)
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{
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if (m_compare(it->first, key))
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{
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return {it, false};
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}
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}
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Container::emplace_back(key, t);
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return {--this->end(), true};
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}
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T& operator[](const Key& key)
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{
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return emplace(key, T{}).first->second;
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}
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const T& operator[](const Key& key) const
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{
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return at(key);
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}
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T& at(const Key& key)
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{
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for (auto it = this->begin(); it != this->end(); ++it)
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{
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if (m_compare(it->first, key))
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{
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return it->second;
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}
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}
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JSON_THROW(std::out_of_range("key not found"));
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}
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const T& at(const Key& key) const
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{
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for (auto it = this->begin(); it != this->end(); ++it)
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{
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if (m_compare(it->first, key))
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{
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return it->second;
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}
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}
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JSON_THROW(std::out_of_range("key not found"));
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}
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size_type erase(const Key& key)
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{
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for (auto it = this->begin(); it != this->end(); ++it)
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{
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if (m_compare(it->first, key))
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{
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// Since we cannot move const Keys, re-construct them in place
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for (auto next = it; ++next != this->end(); ++it)
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{
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it->~value_type(); // Destroy but keep allocation
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new (&*it) value_type{std::move(*next)};
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}
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Container::pop_back();
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return 1;
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}
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}
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return 0;
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}
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iterator erase(iterator pos)
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{
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return erase(pos, std::next(pos));
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}
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iterator erase(iterator first, iterator last)
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{
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const auto elements_affected = std::distance(first, last);
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const auto offset = std::distance(Container::begin(), first);
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// This is the start situation. We need to delete elements_affected
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// elements (3 in this example: e, f, g), and need to return an
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// iterator past the last deleted element (h in this example).
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// Note that offset is the distance from the start of the vector
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// to first. We will need this later.
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// [ a, b, c, d, e, f, g, h, i, j ]
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// ^ ^
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// first last
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// Since we cannot move const Keys, we re-construct them in place.
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// We start at first and re-construct (viz. copy) the elements from
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// the back of the vector. Example for first iteration:
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// ,--------.
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// v | destroy e and re-construct with h
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// [ a, b, c, d, e, f, g, h, i, j ]
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// ^ ^
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// it it + elements_affected
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for (auto it = first; std::next(it, elements_affected) != Container::end(); ++it)
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{
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it->~value_type(); // destroy but keep allocation
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new (&*it) value_type{std::move(*std::next(it, elements_affected))}; // "move" next element to it
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}
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// [ a, b, c, d, h, i, j, h, i, j ]
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// ^ ^
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// first last
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// remove the unneeded elements at the end of the vector
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Container::resize(this->size() - static_cast<size_type>(elements_affected));
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// [ a, b, c, d, h, i, j ]
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// ^ ^
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// first last
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// first is now pointing past the last deleted element, but we cannot
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// use this iterator, because it may have been invalidated by the
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// resize call. Instead, we can return begin() + offset.
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return Container::begin() + offset;
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}
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size_type count(const Key& key) const
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{
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for (auto it = this->begin(); it != this->end(); ++it)
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{
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if (m_compare(it->first, key))
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{
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return 1;
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}
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}
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return 0;
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}
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iterator find(const Key& key)
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{
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for (auto it = this->begin(); it != this->end(); ++it)
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{
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if (m_compare(it->first, key))
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{
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return it;
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}
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}
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return Container::end();
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}
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const_iterator find(const Key& key) const
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{
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for (auto it = this->begin(); it != this->end(); ++it)
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{
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if (m_compare(it->first, key))
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{
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return it;
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}
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}
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return Container::end();
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}
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std::pair<iterator, bool> insert( value_type&& value )
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{
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return emplace(value.first, std::move(value.second));
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}
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std::pair<iterator, bool> insert( const value_type& value )
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{
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for (auto it = this->begin(); it != this->end(); ++it)
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{
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if (m_compare(it->first, value.first))
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{
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return {it, false};
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}
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}
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Container::push_back(value);
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return {--this->end(), true};
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}
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template<typename InputIt>
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using require_input_iter = typename std::enable_if<std::is_convertible<typename std::iterator_traits<InputIt>::iterator_category,
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std::input_iterator_tag>::value>::type;
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template<typename InputIt, typename = require_input_iter<InputIt>>
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void insert(InputIt first, InputIt last)
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{
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for (auto it = first; it != last; ++it)
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{
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insert(*it);
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}
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}
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private:
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JSON_NO_UNIQUE_ADDRESS key_compare m_compare = key_compare();
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};
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} // namespace nlohmann
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