RTTI does more than type-checking

rtti_does_more.cpp

#include <iostream>
#include <type_traits>

class Bird
{
public:
    virtual ~Bird() = default;
};

class IFly
{
public:
    virtual ~IFly() = default;
};

class Swift : public Bird, public IFly
{
};

class Penguin : public Bird
{
};

void perform_various_tests(Bird *bird)
{
    std::cout << "---\n";
    std::cout << "is a swift: " << static_cast<void *>(dynamic_cast<Swift *>(bird)) << "\n";
    std::cout << "is a penguin: " << static_cast<void *>(dynamic_cast<Penguin *>(bird)) << "\n";
    
    // this is where RTTI does more than what we think...
    // it handles pointer offsets!
    std::cout << "can fly: " << static_cast<void *>(dynamic_cast<IFly *>(bird)) << "\n";
}

void verify_convertible(Bird *bird)
{
    std::cout << "---\n";

    std::cout << static_cast<void *>(static_cast<Swift *>(bird)) << "\n";

    // fails to compile
    // std::cout << static_cast<void *>(static_cast<IFly *>(bird)) << "\n";
    
    // will not add offset to pointer if bird == nullptr
    std::cout << static_cast<void *>(static_cast<IFly *>(static_cast<Swift *>(bird))) << "\n";
}

int main()
{
    Swift swift;
    Penguin penguin;

    perform_various_tests(&swift);
    perform_various_tests(&penguin);
    verify_convertible(&swift);

    return 0;
}

// https://godbolt.org/z/3P76oxM3K