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

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bluss:rc-downcast
Sep 17, 2017
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Implement <Rc<Any>>::downcast#44273
bors merged 2 commits intorust-lang:masterfrom
bluss:rc-downcast

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@bluss bluss commented Sep 2, 2017 •
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  • Implement <Rc<Any>>::downcast::<T>
    • New unstable method. Works just like Box<Any>, but for Rc.
    • Any has two cases for its methods: Any and Any + Send; Rc is never Send, so that case is skipped for Rc.
    • Motivation for being a method with self is to match Box and there is no user-supplied type; the inner type is Any and downcast does not conflict with any method of Any.
  • Arc was skipped because Any itself has no downcast for the case that makes most sense: Any + Send + Sync

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rust-highfive commented Sep 2, 2017

r? @sfackler

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bluss commented Sep 2, 2017

I'll probably revise this -- the pointer math in from_raw does not optimize out as it should

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kennytm commented Sep 2, 2017

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.

@bluss
alloc: Implement downcast Rc<Any> -> Rc<T>
758a0ce 
Implement downcast the like it exists for Box.

The implementation avoids using into_raw/from_raw, because the pointer
arithmetic which should cancel does not seem to optimize out at the
moment.

Since Rc<T> is never Send, only Rc<Any> and not Rc<Any + Send>
implements downcast.
@bluss bluss changed the title Implement <Rc<Any>>::downcast and generalize Rc::into_raw Implement <Rc<Any>>::downcast Sep 3, 2017
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bluss commented Sep 3, 2017

I pushed a new version with a more direct implementation, because the pointer arithmetic of using into_raw/from_raw did not optimize out. (playground demo for that)

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bluss commented Sep 3, 2017

@kennytm I'm not sure, there are only four combinations of Any and Send, Sync, so it's simple to cover them all, but a bit confusing in the API doc.

@sfackler sfackler added the T-libs-api Relevant to the library API team, which will review and decide on the PR/issue. label Sep 3, 2017
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sfackler commented Sep 3, 2017

This seems reasonable to me.

@rfcbot fcp merge

@rfcbot rfcbot added the proposed-final-comment-period Proposed to merge/close by relevant subteam, see T-<team> label. Will enter FCP once signed off. label Sep 4, 2017
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rfcbot commented Sep 4, 2017 •
edited by BurntSushi
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Team member @sfackler has proposed to merge this. The next step is review by the rest of the tagged teams:

No concerns currently listed.

Once these reviewers reach consensus, 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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rfcbot commented Sep 13, 2017

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

@rfcbot rfcbot added final-comment-period In the final comment period and will be merged soon unless new substantive objections are raised. and removed proposed-final-comment-period Proposed to merge/close by relevant subteam, see T-<team> label. Will enter FCP once signed off. labels Sep 13, 2017
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alexcrichton commented Sep 14, 2017

@bors: r+

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bors commented Sep 14, 2017

📌 Commit 758a0ce has been approved by alexcrichton

@alexcrichton alexcrichton added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-team labels Sep 14, 2017
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alexcrichton commented Sep 15, 2017

@bors: rollup

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alexcrichton commented Sep 15, 2017

@bors: r-

oh actually, @bluss mind filing a tracking issue for this and updating the PR with that number?

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bluss commented Sep 15, 2017

Sure, updated with tracking issue #44608

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alexcrichton commented Sep 15, 2017

@bors: r+

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bors commented Sep 15, 2017

📌 Commit 3a39d95 has been approved by alexcrichton

alexcrichton added a commit to alexcrichton/rust that referenced this pull request Sep 16, 2017
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Rollup merge of rust-lang#44273 - bluss:rc-downcast, r=alexcrichton
b0e07c6 
Implement <Rc<Any>>::downcast

* Implement `<Rc<Any>>::downcast::<T>`
  * New unstable method. Works just like Box\<Any\>, but for Rc.
  * Any has two cases for its methods: Any and Any + Send; Rc is never Send, so that case is skipped for Rc.
  * Motivation for being a method with self is to match Box and there is no user-supplied type; the inner type is Any and downcast does not conflict with any method of Any.
* Arc was skipped because Any itself has no downcast for the case that makes most sense: Any + Send + Sync
@alexcrichton alexcrichton mentioned this pull request Sep 16, 2017
Closed
frewsxcv added a commit to frewsxcv/rust that referenced this pull request Sep 16, 2017
@frewsxcv
Rollup merge of rust-lang#44273 - bluss:rc-downcast, r=alexcrichton
d04449b 
Implement <Rc<Any>>::downcast

* Implement `<Rc<Any>>::downcast::<T>`
  * New unstable method. Works just like Box\<Any\>, but for Rc.
  * Any has two cases for its methods: Any and Any + Send; Rc is never Send, so that case is skipped for Rc.
  * Motivation for being a method with self is to match Box and there is no user-supplied type; the inner type is Any and downcast does not conflict with any method of Any.
* Arc was skipped because Any itself has no downcast for the case that makes most sense: Any + Send + Sync
@frewsxcv frewsxcv mentioned this pull request Sep 16, 2017
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@alexcrichton alexcrichton mentioned this pull request Sep 16, 2017
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alexcrichton added a commit to alexcrichton/rust that referenced this pull request Sep 17, 2017
@alexcrichton
Rollup merge of rust-lang#44273 - bluss:rc-downcast, r=alexcrichton
2a844b3 
Implement <Rc<Any>>::downcast

* Implement `<Rc<Any>>::downcast::<T>`
  * New unstable method. Works just like Box\<Any\>, but for Rc.
  * Any has two cases for its methods: Any and Any + Send; Rc is never Send, so that case is skipped for Rc.
  * Motivation for being a method with self is to match Box and there is no user-supplied type; the inner type is Any and downcast does not conflict with any method of Any.
* Arc was skipped because Any itself has no downcast for the case that makes most sense: Any + Send + Sync
bors added a commit that referenced this pull request Sep 17, 2017
@bors
Auto merge of #44634 - alexcrichton:rollup, r=alexcrichton
71e3767 
Rollup of 19 pull requests

- Successful merges: #44273, #44356, #44395, #44531, #44537, #44542, #44560, #44567, #44574, #44577, #44586, #44589, #44590, #44593, #44598, #44606, #44609, #44616, #44631
- Failed merges:
@bors bors merged commit 3a39d95 into rust-lang:master Sep 17, 2017
@mbrubeck mbrubeck mentioned this pull request Feb 9, 2018
Closed
@bluss bluss deleted the rc-downcast branch March 17, 2018 16:04
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final-comment-period In the final comment period and will be merged soon unless new substantive objections are raised. S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. T-libs-api Relevant to the library API team, which will review and decide on the PR/issue.

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