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Tracking issue for Rc::downcast (`rc_downcast` feature) #44608

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bluss opened this Issue Sep 15, 2017 · 16 comments

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@bluss @SimonSapin @rfcbot @alexcrichton @jsgf @sfackler @Centril
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bluss commented Sep 15, 2017

Tracking issue for the Rc::downcast method implemented in #44273

@bluss bluss added B-unstable C-tracking-issue T-libs labels Sep 15, 2017

@bluss bluss referenced this issue Sep 15, 2017

Merged

Implement <Rc<Any>>::downcast #44273

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SimonSapin commented Mar 17, 2018

Looks good to me to stabilize.

@rfcbot fcp merge

@rfcbot rfcbot added the proposed-final-comment-period label Mar 17, 2018

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rfcbot commented Mar 17, 2018 •
edited

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

Concerns:

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.
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alexcrichton commented Mar 19, 2018

@rfcbot concern arc

We should add to Arc as well for consistency, right?
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SimonSapin commented Mar 19, 2018

On the implementation PR:

Arc is skipped because Any itself has no downcast for the case that makes most sense: Any + Send + Sync

Why we don't implement downcast for Any + Send + Sync? Other than it isn't terribly necessary.

We can still do that.
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alexcrichton commented Mar 19, 2018

Indeed!
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bluss commented Mar 19, 2018

Hehe, I can't quite find the right way to pick the right implementations.

All four combinations are "Trait", "Trait + Send", "Trait + Sync", "Trait + Send + Sync".

The frugal approach is just the first one for Rc and just the last one for Arc. The perfect would be to write just one that covered them all, for each of Rc and Arc. I think the pragmatic would be all four for both Rc and Arc.
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alexcrichton commented Mar 19, 2018

@bluss I'd be ok conservatively just doing Arc<Any + Send + Sync> as I doubt most other combinations don't actually show up that often in practice
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jsgf commented May 17, 2018

Hi! I ran into this today. Any objections if I put together a PR for Arc<Any + Send + Sync>?
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sfackler commented May 17, 2018

SGTM
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jsgf commented May 17, 2018

Should I reuse this issue and rc_downcast, or create new ones?
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SimonSapin commented May 17, 2018

Using the same tracking issue sounds fine: it’s a identical copy of a fairly small function. By the way, I think you can also remove an unsafe block by using the (relatively) new cast method of NonNull, instead of NonNull::new_unchecked.
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jsgf commented May 17, 2018

I also need to add Any + Send + Sync implementations for is, downcast_ref and Debug to std::any::Any. Do they need feature guards, or can I just insta-stable them? If so, what version would I put in since = "..."?

jsgf added a commit to jsgf/rust that referenced this issue May 17, 2018

@jsgf
Implement `downcast` for `Arc<Any + Send + Sync>` 
We only need to implement it for `Any + Send + Sync` because in practice
that's the only useful combination for `Arc` and `Any`.

Implementation for rust-lang#44608 under the `rc_downcast` feature.
efb5fdc

@jsgf jsgf referenced this issue May 17, 2018

Merged

Arc downcast #50836

jsgf added a commit to jsgf/rust that referenced this issue May 17, 2018

@jsgf
Implement `downcast` for `Arc<Any + Send + Sync>` 
We only need to implement it for `Any + Send + Sync` because in practice
that's the only useful combination for `Arc` and `Any`.

Implementation for rust-lang#44608 under the `rc_downcast` feature.
318a08b

jsgf added a commit to jsgf/rust that referenced this issue May 17, 2018

@jsgf
Implement `downcast` for `Arc<Any + Send + Sync>` 
We only need to implement it for `Any + Send + Sync` because in practice
that's the only useful combination for `Arc` and `Any`.

Implementation for rust-lang#44608 under the `rc_downcast` feature.
a782ae7

jsgf added a commit to jsgf/rust that referenced this issue May 18, 2018

@jsgf
Implement `downcast` for `Arc<Any + Send + Sync>` 
We only need to implement it for `Any + Send + Sync` because in practice
that's the only useful combination for `Arc` and `Any`.

Implementation for rust-lang#44608 under the `rc_downcast` feature.
2e297f2

@Centril Centril added the disposition-merge label May 24, 2018

jsgf added a commit to jsgf/rust that referenced this issue May 31, 2018

@jsgf
Implement `downcast` for `Arc<Any + Send + Sync>` 
We only need to implement it for `Any + Send + Sync` because in practice
that's the only useful combination for `Arc` and `Any`.

Implementation for rust-lang#44608 under the `rc_downcast` feature.
37f5cf5

bors added a commit that referenced this issue Jun 1, 2018

@bors
Auto merge of #50836 - jsgf:arc-downcast, r=SimonSapin 
Arc downcast

Implement `downcast` for `Arc<Any + Send + Sync>` as part of #44608, and gated by the same `rc_downcast` feature.

This PR is mostly lightly-edited cut'n'paste.

This has two additional changes:
- The `downcast` implementation needs `Any + Send + Sync` implementations for `is` and `Debug`, and I added `downcast_ref` and `downcast_mut` for completeness/consistency. (Can these be insta-stabilized?)
- At @SimonSapin's suggestion, I converted `Arc` and `Rc` to use `NonNull::cast` to avoid an `unsafe` block in each which tidied things up nicely.
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SimonSapin commented Jun 6, 2018

@rfcbot resolve arc

The requested feature was implemented in #50836.
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SimonSapin commented Jun 6, 2018 •
edited

Hmm it looks like only @alexcrichton can tell rfcbot to resolve the concern here, but I think we can consider the spirit of the process to be satisfied (if not the letter) and I would accept a stabilization PR. (Alex is away for a month.)

F001 added a commit to F001/rust that referenced this issue Jun 24, 2018

@jsgf @F001
Implement `downcast` for `Arc<Any + Send + Sync>` 
We only need to implement it for `Any + Send + Sync` because in practice
that's the only useful combination for `Arc` and `Any`.

Implementation for rust-lang#44608 under the `rc_downcast` feature.
081274c
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alexcrichton commented Jun 27, 2018

@rfcbot resolved arc

@rfcbot rfcbot added the proposed-final-comment-period label Jun 27, 2018

@rfcbot rfcbot added the disposition-merge label Jun 27, 2018

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rfcbot commented Jun 27, 2018

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

@rfcbot rfcbot added final-comment-period and removed proposed-final-comment-period labels Jun 27, 2018

tmccombs added a commit to tmccombs/rust that referenced this issue Jul 6, 2018

@tmccombs
Stabilize rc_downcast 
Fixes rust-lang#44608
7fbc389

@tmccombs tmccombs referenced this issue Jul 6, 2018

Merged

Stabilize rc_downcast #52103

Mark-Simulacrum added a commit to Mark-Simulacrum/rust that referenced this issue Jul 7, 2018

@Mark-Simulacrum
Rollup merge of rust-lang#52103 - tmccombs:rc_downcast, r=Mark-Simula… 
…crum

Stabilize rc_downcast

Fixes rust-lang#44608
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@bors bors closed this in #52103 Jul 7, 2018

@rfcbot rfcbot added finished-final-comment-period and removed final-comment-period labels Jul 7, 2018

mati865 added a commit to mati865/rust that referenced this issue Jul 24, 2018

@tmccombs @mati865
Stabilize rc_downcast 
Fixes rust-lang#44608
ef45536
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