Unobsolete IPAddress.Address, or create a new equivalent property

[antonfirsov]

Forking #68591 (comment) to a new issue.

IPAddress.Address is the most efficient way to get the IPv4 value, however it doesn't make sense and throws for IPv6, so we made it obsolete.

We should consider unobsoleting it or creating a new, equivalent property with a name that describes the purpose and the limitations better, for example:

public class IPAddress
{
    public long IPv4Value { get; }
}

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Issue Details

---

Forking #68591 (comment) to a new issue.

IPAddress.Address is the most efficient way to get the IPv4 value, however it doesn't make sense and throws for IPv6, so we made it obsolete.

We should consider unobsoleting it or creating a new, equivalent property with a name that describes the purpose and the limitations better, for example:

public class IPAddress
{
    public long IPv4Value { get; }
}

Author:	antonfirsov
Assignees:	-
Labels:	area-System.Net, untriaged
Milestone:	-

[karelz]

Triage: It makes sense -- we should document how it should be used (with IPv4 check).
We should double check with API review team.
We could add analyzer (to check there is IPv4 check) if we think there is problem.

[wfurt]

Would it make sense to have something like

public class IPAddress
{
  int128 GetAddress();
}

While this may be slightly less efficient than long it would preserve simplicity of the old interface and it would also work consistently for IPv6.
cc: @stephentoub as he made the original comment.

[antonfirsov]

@wfurt that is basically #83971, which we decided to close, also implying we would commit to solve #84776 as a prerequisite for such an API to be implemented efficiently. (Otherwise I don't see why would it be better than TryWriteBytes)

[wfurt]

Thanks for the pointer @antonfirsov. That one slipped from my mind. I was fiddling more with IPAddress and IPEndPoint and it would be nice to have the parity. I end up using the TryWriteBytes and it is sufficient but not as slick. Assignments and comparisons all come more complicate not even talking about using Hash.Combine.
I simply used rule to disable the obsolete warning for IPv4 e.g. there was no real functional impact for me - just inconvenience.

Perhaps we should have round of talk with @stephentoub and rest for the team.

[wfurt]

triage: not critical for 9.0, moving to future