From 00d8215e00dedff240fa95f0a7719cd9d4370a25 Mon Sep 17 00:00:00 2001
From: Pavel Labath <pavelo@centrum.sk>
Date: Fri, 12 Feb 2010 17:41:24 +0100
Subject: [PATCH] added state::createuserdata template function

---
 src/luamm.cc |  6 ++----
 src/luamm.hh | 14 ++++++++++++++
 2 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/src/luamm.cc b/src/luamm.cc
index ca73f4b5..bcc24652 100644
--- a/src/luamm.cc
+++ b/src/luamm.cc
@@ -94,10 +94,9 @@ namespace lua {
 			catch(...) {
 				// C++ exceptions (pointers to them, actually) are stored as lua userdata and
 				// then thrown
-				void *ptr = L->newuserdata(sizeof(std::exception_ptr));
+				L->createuserdata<std::exception_ptr>(std::current_exception());
 				L->rawgetfield(REGISTRYINDEX, cpp_exception_metatable);
 				L->setmetatable(-2);
-				new(ptr) std::exception_ptr(std::current_exception());
 			}
 
 			// lua_error does longjmp(), so destructors for objects in this function will not be
@@ -386,10 +385,9 @@ namespace lua {
 	{
 		checkstack(2);
 
-		void *ptr = newuserdata(sizeof(cpp_function));
+		createuserdata<cpp_function>(fn);
 		rawgetfield(REGISTRYINDEX, cpp_function_metatable);
 		setmetatable(-2);
-		new(ptr) cpp_function(fn);
 
 		insert(-n-1);
 		lua_pushcclosure(cobj.get(), &closure_trampoline, n+1);
diff --git a/src/luamm.hh b/src/luamm.hh
index 20101073..3ad38ac8 100644
--- a/src/luamm.hh
+++ b/src/luamm.hh
@@ -263,6 +263,10 @@ namespace lua {
 		// lua_tostring uses NULL to indicate conversion error, since there is no such thing as a
 		// NULL std::string, we throw an exception. Returned value may contain '\0'
 		std::string tostring(int index) throw(lua::not_string_error);
+		// allocate a new lua userdata of appropriate size, and create a object in it
+		// pushes the userdata on stack and returns the pointer
+		template<typename T, typename... Args>
+		T* createuserdata(Args&&... args);
 	};
 
 	/*
@@ -291,6 +295,16 @@ namespace lua {
 		void operator+=(int n_) throw() { n+=n_; }
 		void operator-=(int n_) throw() { n-=n_; }
 	};
+
+	template<typename T, typename... Args>
+	T* state::createuserdata(Args&&... args)
+	{
+		stack_sentry s(*this);
+
+		void *t = newuserdata(sizeof(T)); ++s;
+		new(t) T(std::forward<Args>(args)...); --s;
+		return static_cast<T *>(t);
+	}
 }
 
 #endif /* LUAMM_HH */