🚧 toward an ordered_json type

include/nlohmann/ordered_map.hpp

@@ -0,0 +1,62 @@
+#pragma once
+
+#include <functional> // less
+#include <memory> // allocator
+#include <utility> // pair
+#include <vector> // vector
+
+namespace nlohmann
+{
+
+/// ordered_map: a minimal map-like container that preserves insertion order
+/// for use within nlohmann::basic_json<ordered_map>
+template<class Key, class T, class IgnoredLess = std::less<Key>,
+         class Allocator = std::allocator<std::pair<const Key, T>>,
+         class Container = std::vector<std::pair<const Key, T>, Allocator>>
+struct ordered_map : Container
+{
+    using key_type = Key;
+    using mapped_type = T;
+    using value_type = std::pair<const Key, T>;
+    using Container::Container;
+
+    std::pair<typename Container::iterator, bool> emplace(key_type&& key, T&& t)
+    {
+        for (auto it = this->begin(); it != this->end(); ++it)
+        {
+            if (it->first == key)
+            {
+                return {it, false};
+            }
+        }
+
+        this->emplace_back(key, t);
+        return {--this->end(), true};
+    }
+
+    std::size_t erase(const key_type& key)
+    {
+        std::size_t result = 0;
+        for (auto it = this->begin(); it != this->end();)
+        {
+            if (it->first == key)
+            {
+                ++result;
+                it = Container::erase(it);
+            }
+            else
+            {
+                ++it;
+            }
+        }
+
+        return result;
+    }
+
+    T& operator[](key_type&& key)
+    {
+        return emplace(std::move(key), T{}).first->second;
+    }
+};
+
+}  // namespace nlohmann