Merge pull request #2206 from gatopeich/issue2179
Simple ordered_json that works on all supported compilers
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commit
5f146cb853
5 changed files with 63 additions and 20 deletions
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@ -1527,7 +1527,9 @@ This library will not support comments in the future. If you wish to use comment
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### Order of object keys
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By default, the library does not preserve the **insertion order of object elements**. This is standards-compliant, as the [JSON standard](https://tools.ietf.org/html/rfc8259.html) defines objects as "an unordered collection of zero or more name/value pairs". If you do want to preserve the insertion order, you can specialize the object type with containers like [`tsl::ordered_map`](https://github.com/Tessil/ordered-map) ([integration](https://github.com/nlohmann/json/issues/546#issuecomment-304447518)) or [`nlohmann::fifo_map`](https://github.com/nlohmann/fifo_map) ([integration](https://github.com/nlohmann/json/issues/485#issuecomment-333652309)).
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By default, the library does not preserve the **insertion order of object elements**. This is standards-compliant, as the [JSON standard](https://tools.ietf.org/html/rfc8259.html) defines objects as "an unordered collection of zero or more name/value pairs".
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If you do want to preserve the insertion order, you can try the type [`nlohmann::ordered_json`](https://github.com/nlohmann/json/issues/2179). Alternatively, you can use a more sophisticated ordered map like [`tsl::ordered_map`](https://github.com/Tessil/ordered-map) ([integration](https://github.com/nlohmann/json/issues/546#issuecomment-304447518)) or [`nlohmann::fifo_map`](https://github.com/nlohmann/fifo_map) ([integration](https://github.com/nlohmann/json/issues/485#issuecomment-333652309)).
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### Memory Release
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@ -61,7 +61,7 @@ uses the standard template types.
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*/
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using json = basic_json<>;
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template<class Key, class T, class IgnoredLess, class Allocator, class Container>
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template<class Key, class T, class IgnoredLess, class Allocator>
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struct ordered_map;
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/*!
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@ -11,17 +11,26 @@ namespace nlohmann
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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<Key, T>>,
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class Container = std::vector<std::pair<Key, T>, Allocator>>
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struct ordered_map : Container
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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 value_type = typename Container::value_type;
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using size_type = typename Container::size_type;
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using Container::Container;
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using Container = std::vector<std::pair<const Key, T>, Allocator>;
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using typename Container::iterator;
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using typename Container::size_type;
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using typename Container::value_type;
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std::pair<typename Container::iterator, bool> emplace(key_type&& key, T&& t)
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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(const Allocator& alloc = Allocator()) : 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<T> init, const Allocator& alloc = Allocator() )
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: Container{init, alloc} {}
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std::pair<iterator, bool> emplace(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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@ -45,7 +54,13 @@ struct ordered_map : Container
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{
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if (it->first == key)
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{
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Container::erase(it);
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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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@ -2773,7 +2773,7 @@ uses the standard template types.
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*/
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using json = basic_json<>;
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template<class Key, class T, class IgnoredLess, class Allocator, class Container>
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template<class Key, class T, class IgnoredLess, class Allocator>
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struct ordered_map;
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/*!
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@ -15880,17 +15880,26 @@ namespace nlohmann
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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<Key, T>>,
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class Container = std::vector<std::pair<Key, T>, Allocator>>
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struct ordered_map : Container
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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 value_type = typename Container::value_type;
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using size_type = typename Container::size_type;
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using Container::Container;
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using Container = std::vector<std::pair<const Key, T>, Allocator>;
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using typename Container::iterator;
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using typename Container::size_type;
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using typename Container::value_type;
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std::pair<typename Container::iterator, bool> emplace(key_type&& key, T&& t)
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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(const Allocator& alloc = Allocator()) : 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<T> init, const Allocator& alloc = Allocator() )
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: Container{init, alloc} {}
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std::pair<iterator, bool> emplace(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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@ -15914,7 +15923,13 @@ struct ordered_map : Container
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{
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if (it->first == key)
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{
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Container::erase(it);
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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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@ -16049,7 +16064,7 @@ class basic_json
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InputAdapterType adapter,
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detail::parser_callback_t<basic_json>cb = nullptr,
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bool allow_exceptions = true
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)
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)
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{
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return ::nlohmann::detail::parser<basic_json, InputAdapterType>(std::move(adapter), std::move(cb), allow_exceptions);
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}
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@ -58,4 +58,15 @@ TEST_CASE("ordered_json")
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CHECK(j.dump() == "{\"element2\":2,\"element3\":3}");
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CHECK(oj.dump() == "{\"element3\":3,\"element2\":2}");
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// There are no dup keys cause constructor calls emplace...
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json multi {{"z", 1}, {"m", 2}, {"m", 3}, {"y", 4}, {"m", 5}};
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CHECK(multi.size() == 3);
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CHECK(multi.dump() == "{\"m\":2,\"y\":4,\"z\":1}");
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ordered_json multi_ordered {{"z", 1}, {"m", 2}, {"m", 3}, {"y", 4}, {"m", 5}};
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CHECK(multi_ordered.size() == 3);
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CHECK(multi_ordered.dump() == "{\"z\":1,\"m\":2,\"y\":4}");
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CHECK(multi_ordered.erase("m") == 1);
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CHECK(multi_ordered.dump() == "{\"z\":1,\"y\":4}");
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}
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