Your implementation of IPv6 looks interesting. It's great that you are working on expanding the functionality of IpAddress to support both IPv4 and IPv6. It's a good practice to organize the specific implementations for IPv4 and IPv6 in separate classes like IpAddress::Ipv4 and IpAddress::Ipv6.
If you are considering making a pull request for this implementation, it's important to ensure that your code is well-documented, follows the project's coding standards, and thoroughly tested. This will increase the chances of your pull request being accepted by the project maintainers.
It's also good to see that you have provided a test program along with your implementation. Testing on multiple platforms like Linux and Windows is a good practice to ensure cross-platform compatibility.
Keep up the good work, and don't hesitate to seek feedback or guidance from more experienced developers or the project maintainers if needed. Good luck with your contributions!
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