change expression code so that it evalautes to a reference properly when throwing, otherwise VC++ will return a reference to a value it creates (thanks, VC++ extensions...)

examples/optional_with_iteration.cpp

@@ -0,0 +1,96 @@
+#define SOL_CHECK_ARGUMENTS 1
+
+#include <sol.hpp>
+#include <string>
+#include <memory>
+#include <iostream>
+
+int main(int argc, char** argv) {
+	std::cout << "=== optional and iteration example ===" << std::endl;
+
+	struct thing {
+		int a = 20;
+
+		thing() = default;
+		thing(int a) : a(a) {}
+	};
+
+	struct super_thing : thing {
+		int b = 40;
+	};
+
+	struct unrelated {
+
+	};
+
+	sol::state lua;
+
+	// Comment out the new_usertype call
+	// to prevent derived class "super_thing"
+	// from being picked up and cast to its base
+	// class
+	lua.new_usertype<super_thing>("super_thing",
+		sol::base_classes, sol::bases<thing>()
+	);
+
+	// Make a few things
+	lua["t1"] = thing{};
+	lua["t2"] = super_thing{};
+	lua["t3"] = unrelated{};
+	// And a table
+	lua["container"] = lua.create_table_with(
+		0, thing{50}, 
+		1, unrelated{}, 
+		4, super_thing{}
+	);
+
+
+	std::vector<std::reference_wrapper<thing>> things;
+	// Our recursive function
+	// We use some lambda techniques and pass the function itself itself so we can recurse,
+	// but a regular function would work too!
+	auto fx = [&lua, &things](auto& f, auto& tbl) -> void {
+		// You can iterate through a table: it has 
+		// begin() and end()
+		// like standard containers
+		for (auto key_value_pair : tbl) {
+			// Note that iterators are extremely frail
+			// and should not be used outside of
+			// well-constructed for loops
+			// that use pre-increment ++,
+			// or C++ ranged-for loops
+			const sol::object& key = key_value_pair.first;
+			const sol::object& value = key_value_pair.second;
+			sol::type t = value.get_type();
+			switch (t) {
+			case sol::type::table:
+				f(f, value.as<sol::table>());
+				break;
+			case sol::type::userdata: {
+				// This allows us to check if a userdata is 
+				// a specific class type
+				sol::optional<thing&> maybe_thing = value.as<sol::optional<thing&>>();
+				if (maybe_thing) {
+					thing& the_thing = maybe_thing.value();
+					if (key.is<std::string>()) {
+						std::cout << "key " << key.as<std::string>() << " is a thing -- ";
+					}
+					else if (key.is<int>()) {
+						std::cout << "key " << key.as<int>() << " is a thing -- ";
+					}
+					std::cout << "thing.a ==" << the_thing.a << std::endl;
+					things.push_back(the_thing);
+				}
+			}
+			break;
+			default:
+				break;
+			}
+		}
+	};
+	fx(fx, lua);
+
+	std::cout << std::endl;
+
+	return 0;
+}

sol/optional_implementation.hpp

@@ -771,15 +771,12 @@ namespace sol {
 		}
 
 		constexpr T& value() const {
-			return ref ?
-				*ref
 #ifdef SOL_NO_EXCEPTIONS
-				// we can't abort here
-				// because there's no constexpr abort
-				: *(T*)nullptr;
+			return *ref;
 #else
-				: throw bad_optional_access("bad optional access");
-#endif
+			return ref ? *ref
+			: (throw bad_optional_access("bad optional access"), *ref);
+#endif // Exceptions
 		}
 
 		explicit constexpr operator bool() const noexcept {