+#ifndef _LUA_UTILS_H
+#define _LUA_UTILS_H 1
+
+#include <lauxlib.h>
+#include <lua.hpp>
+
+#include <mutex>
+#include <utility>
+
+class LuaRefWithDeleter {
+public:
+ LuaRefWithDeleter(std::mutex *m, lua_State *L, int ref) : m(m), L(L), ref(ref) {}
+ ~LuaRefWithDeleter() {
+ std::lock_guard<std::mutex> lock(*m);
+ luaL_unref(L, LUA_REGISTRYINDEX, ref);
+ }
+ int get() const { return ref; }
+
+private:
+ LuaRefWithDeleter(const LuaRefWithDeleter &) = delete;
+
+ std::mutex *m;
+ lua_State *L;
+ int ref;
+};
+
+template<class T, class... Args>
+int wrap_lua_object(lua_State* L, const char *class_name, Args&&... args)
+{
+ // Construct the C++ object and put it on the stack.
+ void *mem = lua_newuserdata(L, sizeof(T));
+ new(mem) T(std::forward<Args>(args)...);
+
+ // Look up the metatable named <class_name>, and set it on the new object.
+ luaL_getmetatable(L, class_name);
+ lua_setmetatable(L, -2);
+
+ return 1;
+}
+
+// Like wrap_lua_object, but the object is not owned by Lua; ie. it's not freed
+// by Lua GC. This is typically the case for Effects, which are owned by EffectChain
+// and expected to be destructed by it. The object will be of type T** instead of T*
+// when exposed to Lua.
+//
+// Note that we currently leak if you allocate an Effect in this way and never call
+// add_effect. We should see if there's a way to e.g. set __gc on it at construction time
+// and then release that once add_effect() takes ownership.
+template<class T, class... Args>
+int wrap_lua_object_nonowned(lua_State* L, const char *class_name, Args&&... args)
+{
+ // Construct the pointer ot the C++ object and put it on the stack.
+ T **obj = (T **)lua_newuserdata(L, sizeof(T *));
+ *obj = new T(std::forward<Args>(args)...);
+
+ // Look up the metatable named <class_name>, and set it on the new object.
+ luaL_getmetatable(L, class_name);
+ lua_setmetatable(L, -2);
+
+ return 1;
+}
+
+template<class T>
+int wrap_lua_existing_object_nonowned(lua_State* L, const char *class_name, T *ptr)
+{
+ // Construct the pointer ot the C++ object and put it on the stack.
+ T **obj = (T **)lua_newuserdata(L, sizeof(T *));
+ *obj = ptr;
+
+ // Look up the metatable named <class_name>, and set it on the new object.
+ luaL_getmetatable(L, class_name);
+ lua_setmetatable(L, -2);
+
+ return 1;
+}
+
+#endif // !defined(_LUA_UTILS_H)