Add Ref/RefMut try_map method #118087

GrigorenkoPV · 2023-11-20T09:50:21Z

Tracking issue: #143801

A more generalized version of filter_map, which allows to return some data on failure.

Safety

As far as I can tell, E cannot contain any 'b data, so it is impossible to duplicate the &'b [mut] reference into the RefCell's data.

Other than this E, everything is analogous to the already stable filter_map.

`Try` / `Residual`

I have considered generalizing this to use the Try & Residual just like #79711 does for array::try_map, but it does not seem to be possible: we want to essentially .map_err(|e| (orig, e)) but this does not seem to be supported with Try. (Plus I am not even sure if it is possible to express the fact that &U in Try::Output would have to have the same lifetime as the &T input of F.)

ACP

~~As far as I can tell, this is not mandatory, and the implementation is small enough to probably be smaller than the doc I would have to write.~~

~~rust-lang/libs-team#341~~

rust-lang/libs-team#586

rustbot · 2023-11-20T09:50:30Z

r? @Mark-Simulacrum

(rustbot has picked a reviewer for you, use r? to override)

Mark-Simulacrum · 2023-12-09T14:32:40Z

ACPs are the recommended way to get the libs-api team to approve new unstable APIs. I've marked this as waiting-on-team which I believe also is in their queue.

(libs-api -- we may want to update the guidance on the linked docs to just require an ACP)

m-ou-se · 2023-12-19T15:40:24Z

As far as I can tell, this is not mandatory, and the implementation is small enough to probably be smaller than the doc I would have to write.

The motivation is an important part of the ACP. We do need to understand the motivation, ideally with clear use cases, before accepting new (unstable) APIs.

Dylan-DPC · 2024-02-17T13:14:19Z

@GrigorenkoPV any updates on creating the ACP? if you have done so, kindly add it to the pr description. Thanks

GrigorenkoPV · 2024-02-21T15:34:44Z

The ACP: rust-lang/libs-team#341

@rustbot review

stegaBOB · 2024-11-23T00:11:01Z

Thanks for your work on this @GrigorenkoPV! We would love for this method to be added. @Mark-Simulacrum is there anything else needed here to get it across the finish line? I'd be happy to put some time into this if I can help in any way.

Dylan-DPC · 2024-11-23T12:47:56Z

@stegaBOB this is waiting on the ACP getting merged, so we need to wait fro that and nothing is expected from author or reviewer about it.

bors · 2024-12-09T06:47:54Z

☔ The latest upstream changes (presumably #134052) made this pull request unmergeable. Please resolve the merge conflicts.

GrigorenkoPV · 2024-12-09T10:52:25Z

#133567 changed a place in rustc_interface where this method could be used and now it no longer fits, oh well.

GrigorenkoPV · 2025-07-11T15:29:45Z

rust-lang/libs-team#341 has gone completely unnoticed for a year and a half now, but a slightly more general version of the same API got proposed in rust-lang/libs-team#586 and accepted.

Let me adjust the PR accordingly.

@rustbot author
@rustbot label -S-waiting-on-ACP

rustbot · 2025-07-11T15:29:50Z

Reminder, once the PR becomes ready for a review, use @rustbot ready.

GrigorenkoPV · 2025-08-11T20:15:54Z

@rustbot ready

I've went with the design that does not use Try for two reasons:

Try probably won't be stabilized any time soon
It seems to be impossible to return the original Ref{,Mut} on failure when using Try

Mark-Simulacrum · 2025-08-14T00:16:10Z

@bors r+

bors · 2025-08-14T00:16:13Z

📌 Commit f6bdffd has been approved by Mark-Simulacrum

It is now in the queue for this repository.

…rk-Simulacrum Add Ref/RefMut try_map method Tracking issue: rust-lang#143801 A more generalized version of [`filter_map`](https://doc.rust-lang.org/stable/core/cell/struct.Ref.html#method.filter_map), which allows to return some data on failure. ## Safety As far as I can tell, `E` cannot contain any `'b` data, so it is impossible to duplicate the `&'b [mut]` reference into the `RefCell`'s data. Other than this `E`, everything is analogous to the already stable `filter_map`. ## `Try` / `Residual` I have considered generalizing this to use the `Try` & `Residual` just like rust-lang#79711 does for `array::try_map`, but it does not seem to be possible: we want to essentially `.map_err(|e| (orig, e))` but this does not seem to be supported with `Try`. (Plus I am not even sure if it is possible to express the fact that `&U` in `Try::Output` would have to have the same lifetime as the `&T` input of `F`.) ## ACP ~As far as I can tell, this [is not mandatory](https://std-dev-guide.rust-lang.org/development/feature-lifecycle.html#suitability-for-the-standard-library), and the implementation is small enough to probably be smaller than the doc I would have to write.~ ~rust-lang/libs-team#341 rust-lang/libs-team#586

Rollup of 9 pull requests Successful merges: - #118087 (Add Ref/RefMut try_map method) - #140794 (Add information about group a lint belongs to) - #144947 (Fix description of unsigned `checked_exact_div`) - #145005 (strip prefix of temporary file names when it exceeds filesystem name length limit) - #145233 (cfg_select: Support unbraced expressions) - #145243 (take attr style into account in diagnostics) - #145353 (bootstrap: Fix jemalloc 64K page support for aarch64 tools) - #145379 (bootstrap: Support passing `--timings` to cargo) - #145389 ([rustdoc] Revert "rustdoc search: prefer stable items in search results") Failed merges: - #144983 (Rehome 37 `tests/ui/issues/` tests to other subdirectories under `tests/ui/`) - #145065 (resolve: Introduce `RibKind::Block`) r? `@ghost` `@rustbot` modify labels: rollup

…rk-Simulacrum Add Ref/RefMut try_map method Tracking issue: rust-lang#143801 A more generalized version of [`filter_map`](https://doc.rust-lang.org/stable/core/cell/struct.Ref.html#method.filter_map), which allows to return some data on failure. ## Safety As far as I can tell, `E` cannot contain any `'b` data, so it is impossible to duplicate the `&'b [mut]` reference into the `RefCell`'s data. Other than this `E`, everything is analogous to the already stable `filter_map`. ## `Try` / `Residual` I have considered generalizing this to use the `Try` & `Residual` just like rust-lang#79711 does for `array::try_map`, but it does not seem to be possible: we want to essentially `.map_err(|e| (orig, e))` but this does not seem to be supported with `Try`. (Plus I am not even sure if it is possible to express the fact that `&U` in `Try::Output` would have to have the same lifetime as the `&T` input of `F`.) ## ACP ~As far as I can tell, this [is not mandatory](https://std-dev-guide.rust-lang.org/development/feature-lifecycle.html#suitability-for-the-standard-library), and the implementation is small enough to probably be smaller than the doc I would have to write.~ ~rust-lang/libs-team#341 rust-lang/libs-team#586

Rollup of 22 pull requests Successful merges: - #118087 (Add Ref/RefMut try_map method) - #122661 (Change the desugaring of `assert!` for better error output) - #140740 (Add `-Zindirect-branch-cs-prefix`) - #142640 (Implement autodiff using intrinsics) - #143075 (compiler: Allow `extern "interrupt" fn() -> !`) - #144865 (Fix tail calls to `#[track_caller]` functions) - #144944 (E0793: Clarify that it applies to unions as well) - #144947 (Fix description of unsigned `checked_exact_div`) - #145004 (Couple of minor cleanups) - #145005 (strip prefix of temporary file names when it exceeds filesystem name length limit) - #145012 (Tail call diagnostics to include lifetime info) - #145065 (resolve: Introduce `RibKind::Block`) - #145120 (llvm: Accept new LLVM lifetime format) - #145189 (Weekly `cargo update`) - #145235 (Minor `[const]` tweaks) - #145275 (fix(compiler/rustc_codegen_llvm): apply `target-cpu` attribute) - #145322 (Resolve the prelude import in `build_reduced_graph`) - #145331 (Make std use the edition 2024 prelude) - #145369 (Do not ICE on private type in field of unresolved struct) - #145378 (Add `FnContext` in parser for diagnostic) - #145389 ([rustdoc] Revert "rustdoc search: prefer stable items in search results") - #145392 (coverage: Remove intermediate data structures from mapping creation) r? `@ghost` `@rustbot` modify labels: rollup

…rk-Simulacrum Add Ref/RefMut try_map method Tracking issue: rust-lang#143801 A more generalized version of [`filter_map`](https://doc.rust-lang.org/stable/core/cell/struct.Ref.html#method.filter_map), which allows to return some data on failure. ## Safety As far as I can tell, `E` cannot contain any `'b` data, so it is impossible to duplicate the `&'b [mut]` reference into the `RefCell`'s data. Other than this `E`, everything is analogous to the already stable `filter_map`. ## `Try` / `Residual` I have considered generalizing this to use the `Try` & `Residual` just like rust-lang#79711 does for `array::try_map`, but it does not seem to be possible: we want to essentially `.map_err(|e| (orig, e))` but this does not seem to be supported with `Try`. (Plus I am not even sure if it is possible to express the fact that `&U` in `Try::Output` would have to have the same lifetime as the `&T` input of `F`.) ## ACP ~As far as I can tell, this [is not mandatory](https://std-dev-guide.rust-lang.org/development/feature-lifecycle.html#suitability-for-the-standard-library), and the implementation is small enough to probably be smaller than the doc I would have to write.~ ~rust-lang/libs-team#341 rust-lang/libs-team#586

Rollup of 21 pull requests Successful merges: - #118087 (Add Ref/RefMut try_map method) - #122661 (Change the desugaring of `assert!` for better error output) - #142640 (Implement autodiff using intrinsics) - #143075 (compiler: Allow `extern "interrupt" fn() -> !`) - #144865 (Fix tail calls to `#[track_caller]` functions) - #144944 (E0793: Clarify that it applies to unions as well) - #144947 (Fix description of unsigned `checked_exact_div`) - #145004 (Couple of minor cleanups) - #145005 (strip prefix of temporary file names when it exceeds filesystem name length limit) - #145012 (Tail call diagnostics to include lifetime info) - #145065 (resolve: Introduce `RibKind::Block`) - #145120 (llvm: Accept new LLVM lifetime format) - #145189 (Weekly `cargo update`) - #145235 (Minor `[const]` tweaks) - #145275 (fix(compiler/rustc_codegen_llvm): apply `target-cpu` attribute) - #145322 (Resolve the prelude import in `build_reduced_graph`) - #145331 (Make std use the edition 2024 prelude) - #145369 (Do not ICE on private type in field of unresolved struct) - #145378 (Add `FnContext` in parser for diagnostic) - #145389 ([rustdoc] Revert "rustdoc search: prefer stable items in search results") - #145392 (coverage: Remove intermediate data structures from mapping creation) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of #118087 - GrigorenkoPV:refcell_try_map, r=Mark-Simulacrum Add Ref/RefMut try_map method Tracking issue: #143801 A more generalized version of [`filter_map`](https://doc.rust-lang.org/stable/core/cell/struct.Ref.html#method.filter_map), which allows to return some data on failure. ## Safety As far as I can tell, `E` cannot contain any `'b` data, so it is impossible to duplicate the `&'b [mut]` reference into the `RefCell`'s data. Other than this `E`, everything is analogous to the already stable `filter_map`. ## `Try` / `Residual` I have considered generalizing this to use the `Try` & `Residual` just like #79711 does for `array::try_map`, but it does not seem to be possible: we want to essentially `.map_err(|e| (orig, e))` but this does not seem to be supported with `Try`. (Plus I am not even sure if it is possible to express the fact that `&U` in `Try::Output` would have to have the same lifetime as the `&T` input of `F`.) ## ACP ~As far as I can tell, this [is not mandatory](https://std-dev-guide.rust-lang.org/development/feature-lifecycle.html#suitability-for-the-standard-library), and the implementation is small enough to probably be smaller than the doc I would have to write.~ ~rust-lang/libs-team#341 rust-lang/libs-team#586

rustbot assigned Mark-Simulacrum Nov 20, 2023

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Nov 20, 2023

Amanieu added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-team Status: Awaiting decision from the relevant subteam (see the T-<team> label). labels Dec 19, 2023

Dylan-DPC added the needs-acp This change is blocked on the author creating an ACP. label Feb 17, 2024

GrigorenkoPV mentioned this pull request Feb 21, 2024

ACP: Add {Ref,RefMut}::try_map method rust-lang/libs-team#341

Closed

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Feb 21, 2024

Dylan-DPC added S-waiting-on-ACP Status: PR has an ACP and is waiting for the ACP to complete. and removed needs-acp This change is blocked on the author creating an ACP. S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Feb 22, 2024

GrigorenkoPV force-pushed the refcell_try_map branch from b809d3b to 5ec6988 Compare July 29, 2024 20:28

GrigorenkoPV force-pushed the refcell_try_map branch from 5ec6988 to 59e49ca Compare November 23, 2024 19:23

bors added the S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. label Dec 9, 2024

GrigorenkoPV force-pushed the refcell_try_map branch from 59e49ca to a8dc530 Compare December 9, 2024 10:52

Dylan-DPC removed the S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. label Jan 30, 2025

rustbot added the S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. label Jul 11, 2025

rustbot removed the S-waiting-on-ACP Status: PR has an ACP and is waiting for the ACP to complete. label Jul 11, 2025

GrigorenkoPV mentioned this pull request Jul 11, 2025

Tracking Issue for core::cell::{Ref,RefMut}::try_map #143801

Open

5 tasks

Add Ref/RefMut try_map method

f6bdffd

GrigorenkoPV force-pushed the refcell_try_map branch from a8dc530 to f6bdffd Compare July 11, 2025 23:10

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Aug 11, 2025

bors 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-review Status: Awaiting review from the assignee but also interested parties. labels Aug 14, 2025

GuillaumeGomez mentioned this pull request Aug 14, 2025

Rollup of 9 pull requests #145394

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Zalathar mentioned this pull request Aug 15, 2025

Rollup of 22 pull requests #145418

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Zalathar mentioned this pull request Aug 15, 2025

Rollup of 21 pull requests #145423

Merged

bors merged commit 324bf2b into rust-lang:master Aug 15, 2025
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rustbot added this to the 1.91.0 milestone Aug 15, 2025

GrigorenkoPV deleted the refcell_try_map branch August 15, 2025 18:51

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`Try` / `Residual`