Can now mark json/components with std::optional and then they can be null/false to disable them.

json_mods.hpp

@@ -0,0 +1,34 @@
+#pragma once
+#include <nlohmann/json.hpp>
+#include <nlohmann/json_fwd.hpp>
+#include <optional>
+
+#define ENROLL_COMPONENT(COMPONENT, ...)                         \
+    NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(COMPONENT, __VA_ARGS__);  \
+    template <> struct NameOf<COMPONENT> {                       \
+      static constexpr const char *name = #COMPONENT;            \
+    };
+
+// partial specialization (full specialization works too)
+namespace nlohmann {
+  template <typename T>
+    struct adl_serializer<std::optional<T>> {
+      static void to_json(json& j, const std::optional<T>& opt) {
+        if (opt == std::nullopt) {
+          j = nullptr;
+        } else {
+          j = *opt; // this will call adl_serializer<T>::to_json which will
+          // find the free function to_json in T's namespace!
+        }
+      }
+
+      static void from_json(const json& j, std::optional<T>& opt) {
+        if (j.is_null() || j == false) {
+          opt = std::nullopt;
+        } else {
+          opt = std::make_optional<T>(j.template get<T>());
+          // same as above, but with adl_serializer<T>::from_json
+        }
+      }
+    };
+}