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