sol2/examples/source/read_only.cpp

#define SOL_ALL_SAFETIES_ON 1
#include <sol/sol.hpp>

#include <iostream>

struct object {
	void my_func() {
		std::cout << "hello\n";
	}
};

int deny(lua_State* L) {
	return luaL_error(L, "HAH! Deniiiiied!");
}

int main(int, char*[]) {

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

	object my_obj;

	sol::table obj_table = lua.create_named_table("object");

	sol::table obj_metatable = lua.create_table_with();
	obj_metatable.set_function(
	     "my_func", &object::my_func, &my_obj);
	// Set whatever else you need to
	// on the obj_metatable,
	// not on the obj_table itself!

	// Properly self-index metatable to block things
	obj_metatable[sol::meta_function::new_index] = deny;
	obj_metatable[sol::meta_function::index] = obj_metatable;

	// Set it on the actual table
	obj_table[sol::metatable_key] = obj_metatable;

	try {
		lua.script(R"(
print(object.my_func)
object["my_func"] = 24
print(object.my_func)
        )");
	}
	catch (const std::exception& e) {
		std::cout << "an expected error occurred: " << e.what()
		          << std::endl;
	}
	return 0;
}