Tracking issue for `ToOwned::clone_into` (`toowned_clone_into`)

[scottmcm]

Feature added in PR #41009

Questions raised in the PR:

• The directionality is weird. In clone_from and assignment, the data moves right-to-left, but this moves it left-to-right. And that means that autoref doesn't work well, usually forcing you to write &mut.

• But fixing that would mean putting it somewhere else, since the Self in ToOwned is the wrong type for what this needs to be. And moving it while still being overridable and providing a default is hard.

[SimonSapin]

In nightly for 11 months with no reported issues since. Let’s stabilize.

@rfcbot fcp merge

[rfcbot]

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

• @Kimundi
• @SimonSapin
• @alexcrichton
• @aturon
• @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. 🔔

[scottmcm]

Hmm, I was bad at creating tracking issues a year ago 😅 (fixed)

This is sufficient, but still feels suboptimal for the reasons from #41009 (comment):

• The directionality is weird. In clone_from and assignment, the data moves right-to-left, but this moves it left-to-right. And that means that autoref doesn't work well, usually forcing you to write &mut.

• But fixing that would mean putting it somewhere else, since the Self in ToOwned is the wrong type for what this needs to be. And moving it while still being overridable and providing a default is hard.

Any good ideas?

Edit: Hmm, maybe once we flatten the facade (since Borrow is in core but ToOwned is in alloc) then Borrow could have fn owned_from(&mut self, other: &Borrowed) where Borrowed: ToOwned<Owned=Self> { *self = other.to_owned(); }?

[alexcrichton]

@rfcbot concern direction

formally registering @scottmcm's concern

[rfcbot]

The final comment period is now complete.

[Centril]

@alexcrichton rfcbot did not register the concern :) (the syntax you used is accepted nowadays however..)

[scottmcm]

I feel bad seeing this in TWiR every week now. Anything I can do to help it get somewhere productive?

[kennytm]

Nominating for discussion (how to address the concern raised in #41263 (comment)). ↑.

[SimonSapin]

It looks like this still needs some API some design work, so we’re not actually ready to stabilize.

@rfcbot fcp cancel

This probably needs someone to champion a new API proposal.

[rfcbot]

@SimonSapin proposal cancelled.