funny c++

fun_with_.cpp

#include <iostream>
#include <inttypes.h>

struct Test {
	int x = 55;

	virtual void test() {
		printf("hello %d\n", this->x);
	}
};

struct Test2 : public Test {
	Test2() {
		this->x = 192;
	}

	void test() override {
		printf("goodbye %d\n", this->x);
	}
};

int main() {
	auto* t1 = new Test();
	auto* t2 = new Test2();

	void (*** t2_test_method)(Test*) = reinterpret_cast<void (***)(Test*)>(t2); // get func ptr of Test2 test()
	(**t2_test_method)(t1); // call Test2 test() as a Test instance
	(**t2_test_method)(t2); // call normally

	struct shit_t { // to represent what a test instance would look
		uintptr_t vtable_ptr_space = 0; // the virtual table pointer
		int x = 255; // where x would be
	} shit;

	(**t2_test_method)(reinterpret_cast<Test*>(&shit)); // call the method as if shit was a Test2 instance

	void (* new_vtable[])(Test*) { // create an array of function pointers
		[](Test* this_) {
			printf("hohoho %d", this_->x);
		}
	};

	// make the virtual table pointer point to our array instead
	*reinterpret_cast<uintptr_t*>(t2) = reinterpret_cast<uintptr_t>(new_vtable);

	t2->test(); // calls hohoho
}