Add key_compare member to ordered_map

doc/mkdocs/docs/api/ordered_map.md

@@ -32,6 +32,12 @@ A minimal map-like container that preserves insertion order for use within [`nlo
 - **const_iterator**
 - **size_type**
 - **value_type**
+- **key_compare** - key comparison function
+```cpp
+std::equal_to<Key>  // until C++14
+
+std::equal_to<>     // since C++14
+```
 
 ## Member functions
 
@@ -68,3 +74,4 @@ A minimal map-like container that preserves insertion order for use within [`nlo
 ## Version history
 
 - Added in version 3.9.0 to implement [`nlohmann::ordered_json`](ordered_json.md).
+- Added **key_compare** member in version 3.11.0.

include/nlohmann/ordered_map.hpp

@@ -1,6 +1,6 @@
 #pragma once
 
-#include <functional> // less
+#include <functional> // equal_to, less
 #include <initializer_list> // initializer_list
 #include <iterator> // input_iterator_tag, iterator_traits
 #include <memory> // allocator
@@ -27,6 +27,11 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
     using const_iterator = typename Container::const_iterator;
     using size_type = typename Container::size_type;
     using value_type = typename Container::value_type;
+#ifdef JSON_HAS_CPP_14
+    using key_compare = std::equal_to<>;
+#else
+    using key_compare = std::equal_to<Key>;
+#endif
 
     // Explicit constructors instead of `using Container::Container`
     // otherwise older compilers choke on it (GCC <= 5.5, xcode <= 9.4)

single_include/nlohmann/json.hpp

@@ -17311,7 +17311,7 @@ class serializer
 // #include <nlohmann/ordered_map.hpp>
 
 
-#include <functional> // less
+#include <functional> // equal_to, less
 #include <initializer_list> // initializer_list
 #include <iterator> // input_iterator_tag, iterator_traits
 #include <memory> // allocator
@@ -17339,6 +17339,11 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
     using const_iterator = typename Container::const_iterator;
     using size_type = typename Container::size_type;
     using value_type = typename Container::value_type;
+#ifdef JSON_HAS_CPP_14
+    using key_compare = std::equal_to<>;
+#else
+    using key_compare = std::equal_to<Key>;
+#endif
 
     // Explicit constructors instead of `using Container::Container`
     // otherwise older compilers choke on it (GCC <= 5.5, xcode <= 9.4)