[cxx-interop] Add support for C++ increment decrement operations

[cabmeurer]

Support imported C++ ++ and -- operators in Swift.

Refs #32333

[cabmeurer]

@hyp
@zoecarver

[zoecarver]

@swift-ci please smoke test.

[zoecarver]

This looks great! Thank you!

[zoecarver]

@swift-ci please smoke test.

[zoecarver]

(You don't have to update this PR but) for future PRs, would you mind squashing all your commits into one commit? (Or one commit per "thing," i.e., one commit for increment and one commit for decrement.)

Thanks again for your contribution!

[cabmeurer]

For sure! Happy to help where I can! 🙌

[zoecarver]

Sorry, I didn't read this PR very clearly.

[hyp]

The increment and decrement operators were removed from Swift (https://github.com/apple/swift-evolution/blob/master/proposals/0004-remove-pre-post-inc-decrement.md). I don't think we would want to bring them over from C++ as this doesn't seem Swifty. WDYT @zoecarver ?

[cabmeurer]

I was wondering about that, I had this conversation with another developer. About how the interop could possibly be some what more limited to encourage a "common language overlap". To generally make it easier for swift developers to interact with c++.

[hyp]

I was wondering about that, I had this conversation with another developer. About how the interop could possibly be some what more limited to encourage a "common language overlap". To generally make it easier for swift developers to interact with c++.

That's a good point, but I think we should still err on the side of importing something that Swift has affordances for. I think operators like ++ and -- are valuable when working with iterators for example, but it might be better to bring them over through other means:

• bridging std::next and std::prev can cover a lot of uses cases.
• adding extension to the owning type that match index(after:) and index(before:) would also be a good way to make the iterator increments/decrements Swifty. We might want to bridge the operators in that case to give access to the implementor of the extension, but I could see them being bridged over as some increment/decrement methods on the iterator instead of ++ and --.
  Wdyt?

[cabmeurer]

I was wondering about that, I had this conversation with another developer. About how the interop could possibly be some what more limited to encourage a "common language overlap". To generally make it easier for swift developers to interact with c++.

That's a good point, but I think we should still err on the side of importing something that Swift has affordances for. I think operators like ++ and -- are valuable when working with iterators for example, but it might be better to bring them over through other means:

• bridging std::next and std::prev can cover a lot of uses cases.
• adding extension to the owning type that match index(after:) and index(before:) would also be a good way to make the iterator increments/decrements Swifty. We might want to bridge the operators in that case to give access to the implementor of the extension, but I could see them being bridged over as some increment/decrement methods on the iterator instead of ++ and --.
  Wdyt?

For sure! That sounds like a great approach to me. I will do some more investigating.

Edit: Bridging std::next and std::prev, sounds like a good initial approach, that being said im not super familiar with this space so whatever you think is best.

[hyp]

Thanks! @cabmeurer it might be good to add some test cases that verify that we can bridge over std::next and friends. we can sync up with you on that next.

[cabmeurer]

Thanks! @cabmeurer it might be good to add some test cases that verify that we can bridge over std::next and friends. we can sync up with you on that next.

Awesome! Sounds good