♻ clean up

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

@@ -12,7 +12,6 @@ const_iterator erase(const_iterator first, const_iterator last);
 // (3)
 template<typename KeyT>
 size_type erase(KeyT && key);
-size_type erase(const std::string_view& key); // since C++17
 
 // (4)
 void erase(const size_type idx);
@@ -36,7 +35,7 @@ void erase(const size_type idx);
 ## Template parameters
 
 `KeyT`
-:   A type convertible to an object key. This can also be a string literal.
+:   A type convertible to an object key. This can also be a string literal or a string view (C++17).
 
 ## Parameters
 
@@ -182,4 +181,4 @@ Strong exception safety: if an exception occurs, the original value stays intact
 
 - Added in version 1.0.0.
 - Added support for binary types in version 3.8.0.
-- Added `KeyT` template and overload for `std::string_view` in version 3.10.0.
+- Added `KeyT` template in version 3.10.0.

include/nlohmann/detail/meta/type_traits.hpp

@@ -394,5 +394,17 @@ struct is_constructible_tuple : std::false_type {};
 
 template<typename T1, typename... Args>
 struct is_constructible_tuple<T1, std::tuple<Args...>> : conjunction<std::is_constructible<T1, Args>...> {};
+
+/// type to check if KeyType can be used as object key
+template<typename BasicJsonType, typename KeyType>
+struct is_key_type
+{
+    static constexpr bool value =
+#if defined(JSON_HAS_CPP_17)
+        std::is_same<typename std::decay<KeyType>::type, std::string_view>::value ||
+#endif
+        std::is_convertible<KeyType, typename BasicJsonType::object_t::key_type>::value;
+};
+
 }  // namespace detail
 }  // namespace nlohmann