make sure default userdata_getter does not error everything horribly

update single

examples/interop/Player.h

@@ -0,0 +1,20 @@
+#ifndef PLAYER_H
+#define PLAYER_H
+
+class Player {
+private:
+	int m_health;
+
+public:
+	Player()
+	: m_health(0) {
+	}
+	void setHealth(int health) {
+		m_health - health;
+	}
+	int getHealth() const {
+		return m_health;
+	}
+};
+
+#endif // PLAYER_H

examples/interop/Player.pkg

@@ -0,0 +1,8 @@
+$#include "Player.h"
+
+class Player {
+    Player();
+    ~Player();
+    void setHealth(int _health);
+    int getHealth();
+};

examples/interop/tolua.cpp

@@ -0,0 +1,87 @@
+#define SOL_CHECK_ARGUMENTS 1
+#define SOL_ENABLE_INTEROP 1 // MUST be defined to use interop features
+#include <sol.hpp>
+
+#include "Player.h"
+// pick or replace the includes
+// with whatever generated file you've created
+#include <tolua++.h>
+#include "tolua_Player.h"
+
+#include <iostream>
+#include <cassert>
+
+// tolua code lifted from some blog, if the link dies
+// I don't know where else you're gonna find the reference,
+// http://usefulgamedev.weebly.com/tolua-example.html
+
+namespace sol {
+namespace stack {
+	template <typename T>
+	struct userdata_checker<extensible<T>> {
+		template <typename Handler>
+		static bool check(
+			lua_State* L, int relindex, type index_type, Handler&& handler, record& tracking) {
+			// just marking unused parameters for no compiler warnings
+			(void)index_type;
+			(void)handler;
+			int index = lua_absindex(L, relindex);
+			std::string name = sol::detail::short_demangle<T>();
+			tolua_Error tolua_err;
+			return tolua_isusertype(L, index, name.c_str(), 0, &tolua_err);
+		}
+	};
+}
+} // namespace sol::stack
+
+void register_sol_stuff(lua_State* L) {
+	// grab raw state and put into state_view
+	// state_view is cheap to construct
+	sol::state_view lua(L);
+	// bind and set up your things: everything is entirely self-contained
+	lua["f"] = sol::overload(
+		[](Player& from_tolua) {
+			std::cout << "calling 1-argument version with tolua-created Player { health:" << from_tolua.getHealth() << "}" << std::endl;
+		},
+		[](Player& from_tolua, int second_arg) {
+			std::cout << "calling 2-argument version with tolua-created Player { health: " << from_tolua.getHealth() << "} and integer argument of " << second_arg << std::endl;
+		});
+}
+
+void check_with_sol(lua_State* L) {
+	sol::state_view lua(L);
+	Player& obj = lua["obj"];
+	(void)obj;
+	assert(obj.getHealth() == 4);
+}
+
+int main(int, char* []) {
+
+	std::cout << "=== interop example (tolua) ===" << std::endl;
+	std::cout << "(code lifted from a sol2 user's use case: https://github.com/ThePhD/sol2/issues/511#issuecomment-331729884)" << std::endl;
+
+	lua_State* L = luaL_newstate();
+
+	luaL_openlibs(L);	// initalize all lua standard library functions
+	tolua_open(L);		  // initalize tolua
+	tolua_Player_open(L); // make Player class accessible from LUA
+
+
+	register_sol_stuff(L);
+
+	const auto code = R"(
+obj = Player:new()
+obj:setHealth(4)
+
+f(obj) -- call 1 argument version
+f(obj, 5) -- call 2 argument version
+)";
+
+	if (luaL_dostring(L, code)) {
+		lua_error(L); // crash on error
+	}
+
+	check_with_sol(L);
+
+	return 0;
+}

single/sol/sol.hpp

@@ -20,8 +20,8 @@
 // CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 
 // This file was generated with a script.
-// Generated 2017-09-24 00:26:27.067649 UTC
-// This header was generated with sol v2.18.3 (revision 6d879f5)
+// Generated 2017-09-24 20:03:42.743518 UTC
+// This header was generated with sol v2.18.3 (revision 0c20d06)
 // https://github.com/ThePhD/sol2
 
 #ifndef SOL_SINGLE_INCLUDE_HPP
@@ -6623,6 +6623,15 @@ namespace sol {
 			template <typename T>
 			using strip_t = typename strip<T>::type;
 
+			template <typename T>
+			struct strip_extensible { typedef T type; };
+
+			template <typename T>
+			struct strip_extensible<extensible<T>> { typedef T type; };
+
+			template <typename T>
+			using strip_extensible_t = typename strip_extensible<T>::type;
+
 			const bool default_check_arguments =
 #ifdef SOL_CHECK_ARGUMENTS
 				true;
@@ -7640,8 +7649,10 @@ namespace sol {
 namespace sol {
 namespace stack {
 
-	template <typename T>
-	struct userdata_getter<T> {
+	template <typename U>
+	struct userdata_getter<U> {
+		typedef stack_detail::strip_extensible_t<U> T;
+
 		static std::pair<bool, T*> get(lua_State*, int, void*, record&) {
 			return { false, nullptr };
 		}

sol/stack_core.hpp

@@ -179,6 +179,15 @@ namespace sol {
 			template <typename T>
 			using strip_t = typename strip<T>::type;
 
+			template <typename T>
+			struct strip_extensible { typedef T type; };
+
+			template <typename T>
+			struct strip_extensible<extensible<T>> { typedef T type; };
+
+			template <typename T>
+			using strip_extensible_t = typename strip_extensible<T>::type;
+
 			const bool default_check_arguments =
 #ifdef SOL_CHECK_ARGUMENTS
 				true;

sol/stack_get.hpp

@@ -44,8 +44,10 @@
 namespace sol {
 namespace stack {
 
-	template <typename T>
-	struct userdata_getter<T> {
+	template <typename U>
+	struct userdata_getter<U> {
+		typedef stack_detail::strip_extensible_t<U> T;
+
 		static std::pair<bool, T*> get(lua_State*, int, void*, record&) {
 			return { false, nullptr };
 		}