no make_unexpected with nsel_USES_STD_EXPECTED

[psyinf]

I'm using the library indirectly via BehaviorTree.CPP.
Using a recent clang(17.0.3)/gcc(14.1) the code doesn't compile anymore due to make_unexpected not being available.

I currently patched this locally by adding this into the #if nsel_USES_STD_EXPECTED path (~ line 253):

constexpr auto make_unexpected(E&& value)
{
  return std::unexpected(std::forward<E>(value));
}

If wanted, I can submit a PR with the change or maybe I'm doing something wrong here?

[martinmoene]

Thanks for the heads-up.

Function make_expected() was part of the proposal for std::expected up to and including revision 3 and is available with the nonstd::expected implementation provided nsel_P0323R <= 3 (see section Configuration).

Consequently make_expected() is not available when std::expected is used for nonstd::expected when available and requested as you experience with the recent compilers. Note: in this case it will not help to -Dnsel_P0323R=3

The idea of excpected-lite being a migration path to std::expected, suggests (indeed) that make_expected() and comparison functions should be available in the case of std::expected being used for nonstd::expected AND -Dnsel_P0323R=3 (2 to also include comparison functions).

I'll look into that, unsure how quickly I'll get at it.

[psyinf]

Thanks for looking into it.

The challenge here lies in the expected-lite being used by other libraries taking the liberty in using the P0323R suggested feature throughout their codebase. My suggestion is merely a quick-fix, trying to forward the ´std::unexpected{}´-idiom to the ´make_unexpected´ functionality.

[martinmoene]

I'll add make_expected() unconditionally (assuming nsel_P0323R is already used) for use with std::expected().

Have yet to correct the test suite for use with std::expected, which wasn't yet available at the time of writing.

[martinmoene]

Argh, I now realise it's (also) about make_unexpected()...

Will continue tomorrow.

[psyinf]

@martinmoene Thanks for tackeling the issue. I'll try to the current head in my scenario and advise the authors of BehaviorTree.CPP to use a new release, as soon as available.

[martinmoene]

Currently adapting the test suite for when std:: exception is being used.

Will make a release after that, presumably v0.8.0.

[psyinf]

Just tested compliation with gcc and clang locally, looks good, so the issue can be closed,
Thank you again for the speedy solution

[martinmoene]

Thanks for your feedback & you're welcome.

[martinmoene]

@psyinf Released expected-lite v0.8.0.