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>
This commit is contained in:
Florian Albrechtskirchinger
parent
6df2a1a2cd
commit
0d790397a2
@ -54,11 +54,6 @@ struct is_basic_json_context :
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|| std::is_same<BasicJsonContext, std::nullptr_t>::value >
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{};
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template<typename> struct is_json_pointer : std::false_type {};
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template<typename RefStringType>
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struct is_json_pointer<json_pointer<RefStringType>> : std::true_type {};
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//////////////////////
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// json_ref helpers //
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//////////////////////
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@ -472,6 +467,78 @@ struct is_constructible_tuple : std::false_type {};
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template<typename T1, typename... Args>
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struct is_constructible_tuple<T1, std::tuple<Args...>> : conjunction<is_constructible<T1, Args>...> {};
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template<typename BasicJsonType, typename T>
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struct is_json_iterator_of : std::false_type {};
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template<typename BasicJsonType>
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struct is_json_iterator_of<BasicJsonType, typename BasicJsonType::iterator> : std::true_type {};
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template<typename BasicJsonType>
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struct is_json_iterator_of<BasicJsonType, typename BasicJsonType::const_iterator> : std::true_type
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{};
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// checks if a given type T is a template specialization of Primary
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template<template <typename...> class Primary, typename T>
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struct is_specialization_of : std::false_type {};
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template<template <typename...> class Primary, typename... Args>
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struct is_specialization_of<Primary, Primary<Args...>> : std::true_type {};
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template<typename T>
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using is_json_pointer = is_specialization_of<::nlohmann::json_pointer, uncvref_t<T>>;
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// checks if A and B are comparable using Compare functor
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template<typename Compare, typename A, typename B, typename = void>
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struct is_comparable : std::false_type {};
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template<typename Compare, typename A, typename B>
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struct is_comparable<Compare, A, B, void_t<
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decltype(std::declval<Compare>()(std::declval<A>(), std::declval<B>())),
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decltype(std::declval<Compare>()(std::declval<B>(), std::declval<A>()))
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>> : std::true_type {};
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// checks if BasicJsonType::object_t::key_type and KeyType are comparable using Compare functor
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template<typename BasicJsonType, typename KeyType>
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using is_key_type_comparable = typename is_comparable <
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typename BasicJsonType::object_comparator_t,
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const key_type_t<typename BasicJsonType::object_t>&,
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KeyType >::type;
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template<typename T>
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using detect_is_transparent = typename T::is_transparent;
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// type trait to check if KeyType can be used as object key
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// true if:
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// - KeyType is comparable with BasicJsonType::object_t::key_type
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// - if ExcludeObjectKeyType is true, KeyType is not BasicJsonType::object_t::key_type
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// - the comparator is transparent or RequireTransparentComparator is false
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// - KeyType is not a JSON iterator or json_pointer
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template<typename BasicJsonType, typename KeyTypeCVRef, bool RequireTransparentComparator = true,
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bool ExcludeObjectKeyType = RequireTransparentComparator, typename KeyType = uncvref_t<KeyTypeCVRef>>
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using is_usable_as_key_type = typename std::conditional <
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is_key_type_comparable<BasicJsonType, KeyTypeCVRef>::value
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&& !(ExcludeObjectKeyType && std::is_same<KeyType,
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typename BasicJsonType::object_t::key_type>::value)
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&& (!RequireTransparentComparator || is_detected <
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detect_is_transparent,
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typename BasicJsonType::object_comparator_t >::value)
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&& !is_json_iterator_of<BasicJsonType, KeyType>::value
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&& !is_json_pointer<KeyType>::value,
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std::true_type,
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std::false_type >::type;
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template<typename ObjectType, typename KeyType>
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using detect_erase_with_key_type = decltype(std::declval<ObjectType&>().erase(std::declval<KeyType>()));
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// type trait to check if object_t has an erase() member functions accepting KeyType
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template<typename BasicJsonType, typename KeyType>
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using has_erase_with_key_type = typename std::conditional <
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is_detected <
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detect_erase_with_key_type,
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typename BasicJsonType::object_t, KeyType >::value,
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std::true_type,
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std::false_type >::type;
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// a naive helper to check if a type is an ordered_map (exploits the fact that
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// ordered_map inherits capacity() from std::vector)
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template <typename T>
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@ -3189,11 +3189,6 @@ struct is_basic_json_context :
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|| std::is_same<BasicJsonContext, std::nullptr_t>::value >
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{};
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template<typename> struct is_json_pointer : std::false_type {};
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template<typename RefStringType>
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struct is_json_pointer<json_pointer<RefStringType>> : std::true_type {};
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//////////////////////
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// json_ref helpers //
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//////////////////////
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@ -3607,6 +3602,78 @@ struct is_constructible_tuple : std::false_type {};
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template<typename T1, typename... Args>
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struct is_constructible_tuple<T1, std::tuple<Args...>> : conjunction<is_constructible<T1, Args>...> {};
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template<typename BasicJsonType, typename T>
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struct is_json_iterator_of : std::false_type {};
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template<typename BasicJsonType>
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struct is_json_iterator_of<BasicJsonType, typename BasicJsonType::iterator> : std::true_type {};
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template<typename BasicJsonType>
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struct is_json_iterator_of<BasicJsonType, typename BasicJsonType::const_iterator> : std::true_type
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{};
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// checks if a given type T is a template specialization of Primary
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template<template <typename...> class Primary, typename T>
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struct is_specialization_of : std::false_type {};
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template<template <typename...> class Primary, typename... Args>
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struct is_specialization_of<Primary, Primary<Args...>> : std::true_type {};
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template<typename T>
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using is_json_pointer = is_specialization_of<::nlohmann::json_pointer, uncvref_t<T>>;
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// checks if A and B are comparable using Compare functor
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template<typename Compare, typename A, typename B, typename = void>
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struct is_comparable : std::false_type {};
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template<typename Compare, typename A, typename B>
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struct is_comparable<Compare, A, B, void_t<
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decltype(std::declval<Compare>()(std::declval<A>(), std::declval<B>())),
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decltype(std::declval<Compare>()(std::declval<B>(), std::declval<A>()))
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>> : std::true_type {};
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// checks if BasicJsonType::object_t::key_type and KeyType are comparable using Compare functor
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template<typename BasicJsonType, typename KeyType>
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using is_key_type_comparable = typename is_comparable <
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typename BasicJsonType::object_comparator_t,
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const key_type_t<typename BasicJsonType::object_t>&,
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KeyType >::type;
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template<typename T>
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using detect_is_transparent = typename T::is_transparent;
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// type trait to check if KeyType can be used as object key
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// true if:
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// - KeyType is comparable with BasicJsonType::object_t::key_type
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// - if ExcludeObjectKeyType is true, KeyType is not BasicJsonType::object_t::key_type
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// - the comparator is transparent or RequireTransparentComparator is false
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// - KeyType is not a JSON iterator or json_pointer
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template<typename BasicJsonType, typename KeyTypeCVRef, bool RequireTransparentComparator = true,
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bool ExcludeObjectKeyType = RequireTransparentComparator, typename KeyType = uncvref_t<KeyTypeCVRef>>
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using is_usable_as_key_type = typename std::conditional <
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is_key_type_comparable<BasicJsonType, KeyTypeCVRef>::value
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&& !(ExcludeObjectKeyType && std::is_same<KeyType,
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typename BasicJsonType::object_t::key_type>::value)
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&& (!RequireTransparentComparator || is_detected <
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detect_is_transparent,
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typename BasicJsonType::object_comparator_t >::value)
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&& !is_json_iterator_of<BasicJsonType, KeyType>::value
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&& !is_json_pointer<KeyType>::value,
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std::true_type,
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std::false_type >::type;
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template<typename ObjectType, typename KeyType>
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using detect_erase_with_key_type = decltype(std::declval<ObjectType&>().erase(std::declval<KeyType>()));
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// type trait to check if object_t has an erase() member functions accepting KeyType
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template<typename BasicJsonType, typename KeyType>
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using has_erase_with_key_type = typename std::conditional <
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is_detected <
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detect_erase_with_key_type,
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typename BasicJsonType::object_t, KeyType >::value,
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std::true_type,
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std::false_type >::type;
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// a naive helper to check if a type is an ordered_map (exploits the fact that
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// ordered_map inherits capacity() from std::vector)
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template <typename T>
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