[boost] [outcome v2] ntkernel_category() custom error category appropriate for Outcome?

[Niall Douglas via Boost]

I put together a custom `std::error_category` for NT kernel `NTSTATUS`
error codes with error condition comparison support for both POSIX and
Win32 error code spaces:

https://github.com/ned14/ntkernel-error-category

Question: Is this custom `std::error_category` so niche and unlikely to
be useful to anybody that people would object to it being supplied in
Outcome v2?

Niall

[Gavin Lambert via Boost]

Post by Niall Douglas via Boost
I put together a custom `std::error_category` for NT kernel `NTSTATUS`
error codes with error condition comparison support for both POSIX and
https://github.com/ned14/ntkernel-error-category

I do like that this allows interpretation of NTSTATUS codes on
non-Windows, although the chances of actually encountering one in that
case seems rather slim (unless maybe CIFS APIs expose the raw server
status code).

Post by Niall Douglas via Boost
Question: Is this custom `std::error_category` so niche and unlikely to
be useful to anybody that people would object to it being supplied in
Outcome v2?

Isn't Outcome v2 header-only?

It seems weird to add this to it in that case (because this prefers to
build as a shared library).

Much as it seems cumbersome to have such a small library be standalone,
I think that might be the better choice, rather than changing a
completely-header-only library into an only-kinda-header-only library.


On the other hand, the exported-inline pattern *does* work (at least on
Windows) to make real singletons between shared libraries even from
header-only -- you just need to let the user pick one library to export
the definition and ensure all consumers of that library import it.
Presumably Linux/gcc has an equivalent?


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[Niall Douglas via Boost]

Post by Gavin Lambert via Boost

Post by Niall Douglas via Boost
I put together a custom `std::error_category` for NT kernel `NTSTATUS`
error codes with error condition comparison support for both POSIX and
https://github.com/ned14/ntkernel-error-category

I do like that this allows interpretation of NTSTATUS codes on
non-Windows, although the chances of actually encountering one in that
case seems rather slim (unless maybe CIFS APIs expose the raw server
status code).

I was more thinking of log parsers actually. So the log can dump raw
NTSTATUS codes on Windows, and portable code can parse that log on any
platform. Still very niche though.

Post by Gavin Lambert via Boost

Post by Niall Douglas via Boost
Question: Is this custom `std::error_category` so niche and unlikely to
be useful to anybody that people would object to it being supplied in
Outcome v2?

Isn't Outcome v2 header-only?
It seems weird to add this to it in that case (because this prefers to
build as a shared library).

Fair point. The ntkernel-error-category DLL is several hundred Kb in
size. It's definitely better as a shared library.

Post by Gavin Lambert via Boost
On the other hand, the exported-inline pattern *does* work (at least on
Windows) to make real singletons between shared libraries even from
header-only -- you just need to let the user pick one library to export
the definition and ensure all consumers of that library import it.
Presumably Linux/gcc has an equivalent?

It's tricky on both POSIX and Windows to get right, and most don't need
to bother with perfect correctness. But that's the case for any C or C++
library that implements unique singletons, it's just unusual that you
actually really do need to get it right else error condition comparisons
will randomly fail.

Niall