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Niels Lohmann
cc6d74feb0
With JSON_BRACE_INIT_COPY_SEMANTICS enabled, single-element brace
initialization from a JSON value decided whether to copy the value or
build an object by inspecting the value's runtime shape: a two-element
array whose first element is a string, such as ["key", 42], was turned
into an object instead of being copied. This made the behavior depend
on the element's content, and it did not distinguish an existing value
of this shape from a nested braced pair written in the source, such as
the inner {"key", "value"} of {{"key", "value"}}.
json_ref now records whether it was constructed from a braced list
(true only for the std::initializer_list<json_ref> constructor used
for nested braced lists) or from a value. The initializer-list
constructor uses this to copy or move a single non-braced-list element
before deciding whether the list describes an object, so a JSON value
is always copied regardless of its shape, while a braced pair written
in the source still creates an object.
Fixes #5662.
Signed-off-by: Niels Lohmann <mail@nlohmann.me>
88 lines
2.0 KiB
C++
88 lines
2.0 KiB
C++
// __ _____ _____ _____
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// __| | __| | | | JSON for Modern C++
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// | | |__ | | | | | | version 3.12.0
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// |_____|_____|_____|_|___| https://github.com/nlohmann/json
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//
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// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
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// SPDX-License-Identifier: MIT
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#pragma once
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#include <initializer_list>
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#include <utility>
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#include <nlohmann/detail/abi_macros.hpp>
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#include <nlohmann/detail/meta/type_traits.hpp>
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NLOHMANN_JSON_NAMESPACE_BEGIN
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namespace detail
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{
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template<typename BasicJsonType>
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class json_ref
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{
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public:
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using value_type = BasicJsonType;
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json_ref(value_type&& value)
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: owned_value(std::move(value))
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{}
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json_ref(const value_type& value)
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: value_ref(&value)
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{}
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json_ref(std::initializer_list<json_ref> init)
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: owned_value(init)
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, braced_list(true)
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{}
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template <
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class... Args,
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enable_if_t<std::is_constructible<value_type, Args...>::value, int> = 0 >
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json_ref(Args && ... args)
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: owned_value(std::forward<Args>(args)...)
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{}
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// class should be movable only
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json_ref(json_ref&&) noexcept = default;
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json_ref(const json_ref&) = delete;
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json_ref& operator=(const json_ref&) = delete;
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json_ref& operator=(json_ref&&) = delete;
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~json_ref() = default;
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value_type moved_or_copied() const
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{
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if (value_ref == nullptr)
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{
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return std::move(owned_value);
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}
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return *value_ref;
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}
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value_type const& operator*() const
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{
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return value_ref ? *value_ref : owned_value;
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}
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value_type const* operator->() const
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{
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return &** this;
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}
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/// whether the value was written as a braced list, such as {"key", 1},
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/// rather than given as a value
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bool is_braced_list() const noexcept
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{
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return braced_list;
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}
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private:
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mutable value_type owned_value = nullptr;
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value_type const* value_ref = nullptr;
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bool braced_list = false;
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};
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} // namespace detail
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NLOHMANN_JSON_NAMESPACE_END
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