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#define SOL_ALL_SAFETIES_ON 1
#include <sol/sol.hpp>
#include <map>
#include <iostream>
struct my_thing {
std::map<std::string, int> m{
{ "bark", 20 },
{ "woof", 60 },
{ "borf", 30 },
{ "awoo", 5 },
};
my_thing() {
}
};
struct lua_iterator_state {
typedef std::map<std::string, int>::iterator it_t;
it_t it;
it_t last;
lua_iterator_state(my_thing& mt) : it(mt.m.begin()), last(mt.m.end()) {}
};
std::tuple<sol::object, sol::object> my_next(sol::user<lua_iterator_state&> user_it_state, sol::this_state l) {
// this gets called
// to start the first iteration, and every
// iteration there after
// the state you passed in my_pairs is argument 1
// the key value is argument 2, but we do not
// care about the key value here
lua_iterator_state& it_state = user_it_state;
auto& it = it_state.it;
if (it == it_state.last) {
// return nil to signify that
// there's nothing more to work with.
return std::make_tuple(
sol::object(sol::lua_nil),
sol::object(sol::lua_nil)
);
}
auto itderef = *it;
// 2 values are returned (pushed onto the stack):
// the key and the value
// the state is left alone
auto r = std::make_tuple(sol::object(l, sol::in_place, it->first), sol::object(l, sol::in_place, it->second));
// the iterator must be moved forward one before we return
std::advance(it, 1);
return r;
}
auto my_pairs(my_thing& mt) {
// pairs expects 3 returns:
// the "next" function on how to advance,
// the "table" itself or some state,
// and an initial key value (can be nil)
// prepare our state
lua_iterator_state it_state(mt);
// sol::user is a space/time optimization over regular usertypes,
// it's incompatible with regular usertypes and stores the type T directly in lua without any pretty setup
// saves space allocation and a single dereference
return std::make_tuple(&my_next, sol::user<lua_iterator_state>(std::move(it_state)), sol::lua_nil);
}
int main(int, char*[]) {
std::cout << "===== pairs (advanced) =====" << std::endl;
sol::state lua;
lua.open_libraries(sol::lib::base);
lua.new_usertype<my_thing>("my_thing",
sol::meta_function::pairs, my_pairs
);
#if SOL_LUA_VERSION > 501
lua.safe_script(R"(
local mt = my_thing.new()
for k, v in pairs(mt) do
print(k, v)
end
)");
#endif // Does not work on Lua 5.1
std::cout << std::endl;
return 0;
}
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