Referential transparency is important.

sol/container_usertype_metatable.hpp

@@ -105,7 +105,7 @@ namespace sol {
 				if (k <= src.size() && k > 0) {
 					--k;
 					std::advance(it, k);
-					return stack::push(L, *it);
+					return stack::push_reference(L, *it);
 				}
 			}
 			return stack::push(L, nil);
@@ -115,7 +115,7 @@ namespace sol {
 			K k = stack::get<K>(L, 2);
 			--k;
 			std::advance(it, k);
-			return stack::push(L, *it);
+			return stack::push_reference(L, *it);
 #endif // Safety
 		}
 
@@ -164,8 +164,7 @@ namespace sol {
 			if (it == end(source)) {
 				return 0;
 			}
-			int p = stack::push(L, k + 1);
-			p += stack::push(L, *it);
+			int p = stack::multi_push_reference(L, k + 1, *it);
 			std::advance(it, 1);
 			return p;
 		}
@@ -262,7 +261,7 @@ namespace sol {
 				auto it = detail::find(src, *k);
 				if (it != end(src)) {
 					auto& v = *it;
-					return stack::push(L, v.second);
+					return stack::push_reference(L, v.second);
 				}
 			}
 			return stack::push(L, nil);

sol/simple_usertype_metatable.hpp

@@ -282,7 +282,7 @@ namespace sol {
 			indexbase(&usertype_detail::simple_core_indexing_call<true>), newindexbase(&usertype_detail::simple_core_indexing_call<false>),
 			indexbaseclasspropogation(usertype_detail::walk_all_bases<true>), newindexbaseclasspropogation(&usertype_detail::walk_all_bases<false>),
 			baseclasscheck(nullptr), baseclasscast(nullptr),
-			mustindex(false), secondarymeta(false) {
+			mustindex(true), secondarymeta(true) {
 			(void)detail::swallow{ 0,
 				(add(L, detail::forward_get<I * 2>(args), detail::forward_get<I * 2 + 1>(args)),0)...
 			};

test_containers.cpp

@@ -272,3 +272,39 @@ TEST_CASE("containers/arbitrary-creation", "userdata and tables should be usable
 	REQUIRE(c.get<std::string>("name") == "Rapptz");
 	REQUIRE(c.get<std::string>("project") == "sol");
 }
+
+TEST_CASE("containers/usertype-transparency", "Make sure containers pass their arguments through transparently and push the results as references, not new values") {
+	class A {
+	public:
+		int a;
+		A(int b = 2) : a(b) {};
+
+		void func() { }
+	};
+
+	struct B {
+
+		B() {
+			for (std::size_t i = 0; i < 20; ++i) {
+				a_list.emplace_back(static_cast<int>(i));
+			}
+		}
+
+		std::vector<A> a_list;
+	};
+
+	sol::state lua;
+	lua.new_usertype<B>("B",
+		"a_list", &B::a_list
+		);
+
+	lua.script(R"(
+b = B.new()
+a_ref = b.a_list[2]
+)");
+
+	B& b = lua["b"];
+	A& a_ref = lua["a_ref"];
+	REQUIRE(&b.a_list[1] == &a_ref);
+	REQUIRE(b.a_list[1].a == a_ref.a);
+}

test_simple_usertypes.cpp

@@ -437,3 +437,23 @@ TEST_CASE("usertype/simple-destruction-test", "make sure usertypes are properly
 		lua["testCrash"]();
 	}
 }
+
+TEST_CASE("usertype/simple-table-append", "Ensure that appending to the meta table also affects the internal function table for pointers as well") {
+	struct A {
+		int func() {
+			return 5000;
+		}
+	};
+
+	sol::state lua;
+	lua.open_libraries();
+
+	lua.new_simple_usertype<A>("A");
+	sol::table table = lua["A"];
+	table["func"] = &A::func;
+	A a;
+	lua.set("a", &a);
+	REQUIRE_NOTHROW(
+		lua.script("assert(a:func() == 5000)")
+	);
+}