#define SOL_ALL_SAFETIES_ON 1

#include <sol/sol.hpp>

#include <iostream>

#include <unordered_map>

// use as-is,

// add as a member of your class,

// or derive from it and bind it appropriately

struct dynamic_object {

std::unordered_map<std::string, sol::object> entries;

void dynamic_set(std::string key, sol::stack_object value) {

auto it = entries.find(key);

if (it == entries.cend()) {

entries.insert(

it, { std::move(key), std::move(value) });

}

else {

std::pair<const std::string, sol::object>& kvp

= *it;

sol::object& entry = kvp.second;

entry = sol::object(std::move(value));

}

}

sol::object dynamic_get(std::string key) {

auto it = entries.find(key);

if (it == entries.cend()) {

return sol::lua_nil;

}

return it->second;

}

};

int main() {

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

sol::state lua;

lua.open_libraries(sol::lib::base);

lua.new_usertype<dynamic_object>("dynamic_object",

sol::meta_function::index,

&dynamic_object::dynamic_get,

sol::meta_function::new_index,

&dynamic_object::dynamic_set,

sol::meta_function::length,

[](dynamic_object& d) { return d.entries.size(); });

lua.safe_script(R"(

d1 = dynamic_object.new()

d2 = dynamic_object.new()

print(#d1) -- length operator

print(#d2)

function d2:run(lim)

local r = 0

for i=0,lim do

r = r + i

end

if (r % 2) == 1 then

print("odd")

end

return r

end

-- only added an entry to d2

print(#d1)

print(#d2)

-- only works on d2

local value = d2:run(5)

assert(value == 15)

)");

// does not work on d1: 'run' wasn't added to d1, only d2

auto script_result = lua.safe_script(

"local value = d1:run(5)", sol::script_pass_on_error);

sol_c_assert(!script_result.valid());

sol::error err = script_result;

std::cout << "received expected error: " << err.what()

<< std::endl;

std::cout << std::endl;

return 0;

}