128 lines
3.7 KiB
C++
128 lines
3.7 KiB
C++
#pragma once
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#include <cstddef> // size_t
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#include <string> // string, to_string
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#include <iterator> // input_iterator_tag
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#include <nlohmann/detail/value_t.hpp>
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namespace nlohmann
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{
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namespace detail
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{
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/// proxy class for the items() function
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template<typename IteratorType> class iteration_proxy
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{
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private:
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/// helper class for iteration
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class iteration_proxy_internal
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{
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public:
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using difference_type = std::ptrdiff_t;
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using value_type = iteration_proxy_internal;
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using pointer = iteration_proxy_internal*;
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using reference = iteration_proxy_internal&;
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using iterator_category = std::input_iterator_tag;
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private:
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/// the iterator
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IteratorType anchor;
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/// an index for arrays (used to create key names)
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std::size_t array_index = 0;
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/// last stringified array index
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mutable std::size_t array_index_last = 0;
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/// a string representation of the array index
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mutable std::string array_index_str = "0";
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/// an empty string (to return a reference for primitive values)
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const std::string empty_str = "";
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public:
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explicit iteration_proxy_internal(IteratorType it) noexcept : anchor(it) {}
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iteration_proxy_internal(const iteration_proxy_internal&) = default;
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iteration_proxy_internal& operator=(const iteration_proxy_internal&) = default;
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/// dereference operator (needed for range-based for)
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iteration_proxy_internal& operator*()
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{
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return *this;
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}
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/// increment operator (needed for range-based for)
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iteration_proxy_internal& operator++()
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{
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++anchor;
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++array_index;
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return *this;
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}
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/// equality operator (needed for InputIterator)
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bool operator==(const iteration_proxy_internal& o) const noexcept
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{
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return anchor == o.anchor;
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}
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/// inequality operator (needed for range-based for)
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bool operator!=(const iteration_proxy_internal& o) const noexcept
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{
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return anchor != o.anchor;
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}
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/// return key of the iterator
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const std::string& key() const
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{
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assert(anchor.m_object != nullptr);
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switch (anchor.m_object->type())
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{
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// use integer array index as key
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case value_t::array:
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{
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if (array_index != array_index_last)
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{
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array_index_str = std::to_string(array_index);
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array_index_last = array_index;
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}
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return array_index_str;
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}
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// use key from the object
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case value_t::object:
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return anchor.key();
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// use an empty key for all primitive types
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default:
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return empty_str;
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}
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}
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/// return value of the iterator
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typename IteratorType::reference value() const
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{
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return anchor.value();
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}
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};
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/// the container to iterate
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typename IteratorType::reference container;
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public:
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/// construct iteration proxy from a container
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explicit iteration_proxy(typename IteratorType::reference cont) noexcept
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: container(cont) {}
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/// return iterator begin (needed for range-based for)
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iteration_proxy_internal begin() noexcept
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{
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return iteration_proxy_internal(container.begin());
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}
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/// return iterator end (needed for range-based for)
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iteration_proxy_internal end() noexcept
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{
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return iteration_proxy_internal(container.end());
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}
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};
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}
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}
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