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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()) {}
};
int my_next(lua_State* L) {
// this gets called
// to start the first iteration, and every
// iteration there after
// the state you passed in pairs is argument 1
// the key value is argument 2
// we do not care about the key value here
lua_iterator_state& it_state = sol::stack::get<sol::user<lua_iterator_state>>(L, 1);
auto& it = it_state.it;
if (it == it_state.last) {
return sol::stack::push(L, sol::lua_nil);
}
auto itderef = *it;
// 2 values are returned (pushed onto the stack):
// the key and the value
// the state is left alone
int pushed = sol::stack::push(L, itderef.first);
pushed += sol::stack::push_reference(L, itderef.second);
std::advance(it, 1);
return pushed;
}
int my_pairs(lua_State* L) {
my_thing& mt = sol::stack::get<my_thing>(L, 1);
lua_iterator_state it_state(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)
// next function controls iteration
int pushed = sol::stack::push(L, my_next);
pushed += sol::stack::push<sol::user<lua_iterator_state>>(L, std::move(it_state));
pushed += sol::stack::push(L, sol::lua_nil);
return pushed;
}
int main(int, char*[]) {
std::cout << "===== pairs (using raw Lua C functions) (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 and below
std::cout << std::endl;
return 0;
}
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