holy() : data() {}

holy(int value) : data(value) {}

~holy() {}

struct deleter {

void operator()(holy* p) const {

destroy(*p);

}

};

const int data;

static std::unique_ptr<holy, deleter> create() {

std::cout << "creating 'holy' unique_ptr directly and letting sol/Lua handle it" << std::endl;

return std::unique_ptr<holy, deleter>(new holy(50));

}

static void initialize(holy& uninitialized_memory) {

std::cout << "initializing 'holy' userdata at " << static_cast<void*>(&uninitialized_memory) << std::endl;

// receive uninitialized memory from Lua:

// properly set it by calling a constructor

// on it

// "placement new"

new (&uninitialized_memory) holy();

}

static void destroy(holy& memory_from_lua) {

std::cout << "destroying 'holy' userdata at " << static_cast<void*>(&memory_from_lua) << std::endl;

memory_from_lua.~holy();

}

std::cout << "=== usertype_initializers ===" << std::endl;

{ // additional scope to make usertype destroy earlier

sol::state lua;

lua.open_libraries();

lua.new_usertype<holy>("holy",

"new", sol::initializers(&holy::initialize),

"create", sol::factories(&holy::create),

sol::meta_function::garbage_collect, sol::destructor(&holy::destroy),

"data", &holy::data

);

lua.script(R"(

)");

holy& h1 = lua["h1"];

holy& h2 = lua["h2"];

c_assert(h1.data == 50);

c_assert(h2.data == 0);

}

std::cout << std::endl;

}