RFC: Selfexhausting iter adapter

[Emerentius]

Rendered

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Add an adapter .exhausting() to Iterator which causes the iterator to be driven to its end on drop. Before dropping it will act exactly like the source iterator.

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One of two RFCs for splitting the functionality of drain into two orthogonal APIs.
Other RFC: #2369

[scottmcm]

Why always external iteration? What would keep it from doing internal iteration with try_fold?

[Emerentius]

You're right. I was confused about internal iteration and the requirement for consumption.

[main--]

Add exhausting to the FusedIterator trait to side-step the issue of non-fused iterators altogether.

Note that the flag workaround you propose in the drawbacks section is basically a reimplementation of core::iter::Fuse<I>. I think this clearly shows that this API is designed/"wants to" work with fused iterators only, so I'm very much in favor of this alternative.

[SimonSapin]

Thank you for writing this RFC! The libs team discussed this today, and we felt that this seems too niche of a functionality and that the motivation seemed too weak, especially with the accompanying non-exhausting-drain RFC being postponed for a future unified design that includes other functionality such as filtering-drain.

So we’ll likely not add this to the standard library at this time:

@rfcbot fcp close

Consider experimenting with this API in a crate, possibly in https://crates.io/crates/itertools.

[rfcbot]

Team member @SimonSapin has proposed to close this. The next step is review by the rest of the tagged teams:

• @Kimundi
• @SimonSapin
• @alexcrichton
• @dtolnay
• @sfackler
• @withoutboats

No concerns currently listed.

Once a majority of reviewers approve (and none object), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

See this document for info about what commands tagged team members can give me.

[rfcbot]

🔔 This is now entering its final comment period, as per the review above. 🔔

[Emerentius]

I had forgotten this was still open. It's a good idea to close it for now. I might bring it up again, if it fits together with an improved generalized drain.
I'll cut this short and just close it directly.