Implement flatten for `Option<&Option<T>>` and `Option<&mut Option<T>>` #108671

Coca162 · 2023-03-02T19:15:19Z

Adds .flatten_ref() to get a immutable reference of a nested option and .flatten_mut() for mutable references.

ACP: rust-lang/libs-team#186
Tracking Issue: #149221

rustbot · 2023-03-02T19:15:30Z

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rustbot · 2023-03-02T19:15:36Z

Hey! It looks like you've submitted a new PR for the library teams!

If this PR contains changes to any rust-lang/rust public library APIs then please comment with @rustbot label +T-libs-api -T-libs to tag it appropriately. If this PR contains changes to any unstable APIs please edit the PR description to add a link to the relevant API Change Proposal or create one if you haven't already. If you're unsure where your change falls no worries, just leave it as is and the reviewer will take a look and make a decision to forward on if necessary.

Examples of T-libs-api changes:

Stabilizing library features
Introducing insta-stable changes such as new implementations of existing stable traits on existing stable types
Introducing new or changing existing unstable library APIs (excluding permanently unstable features / features without a tracking issue)
Changing public documentation in ways that create new stability guarantees
Changing observable runtime behavior of library APIs

cuviper · 2023-03-02T19:33:03Z

Please do create an API Change Proposal as linked above.

@rustbot label +T-libs-api -T-libs
r? libs-api

compiler/rustc_feature/src/active.rs

joshtriplett · 2024-02-11T03:03:49Z

r? libs-api

bors · 2024-10-02T06:54:50Z

☔ The latest upstream changes (presumably #130829) made this pull request unmergeable. Please resolve the merge conflicts.

…T>>`

rustbot · 2025-11-22T17:31:39Z

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

Coca162 · 2025-12-18T22:13:54Z

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

dtolnay

Thanks!

View changes since this review

dtolnay · 2025-12-28T23:24:33Z

@bors r+

bors · 2025-12-28T23:24:35Z

📌 Commit 0e54845 has been approved by dtolnay

It is now in the queue for this repository.

bors · 2025-12-29T02:12:52Z

⌛ Testing commit 0e54845 with merge 123588a...

bors · 2025-12-29T05:33:26Z

☀️ Test successful - checks-actions
Approved by: dtolnay
Pushing 123588a to main...

github-actions · 2025-12-29T05:36:28Z

What is this?

This is an experimental post-merge analysis report that shows differences in test outcomes between the merged PR and its parent PR.

Comparing 7fefa09 (parent) -> 123588a (this PR)

Test differences

Show 14 test diffs

14 doctest diffs were found. These are ignored, as they are noisy.

Test dashboard

Run

cargo run --manifest-path src/ci/citool/Cargo.toml -- \
    test-dashboard 123588a5bf9250f214e1931a761f814660e69620 --output-dir test-dashboard

And then open test-dashboard/index.html in your browser to see an overview of all executed tests.

Job duration changes

dist-aarch64-apple: 6361.2s -> 7172.9s (+12.8%)
x86_64-gnu-llvm-20: 4437.7s -> 4987.0s (+12.4%)
x86_64-gnu-llvm-20-3: 7314.0s -> 6444.5s (-11.9%)
tidy: 184.8s -> 165.1s (-10.7%)
aarch64-msvc-2: 6524.4s -> 5851.9s (-10.3%)
x86_64-gnu-stable: 8749.0s -> 7956.7s (-9.1%)
dist-x86_64-msvc-alt: 9163.2s -> 9956.1s (+8.7%)
dist-aarch64-msvc: 6240.1s -> 5776.2s (-7.4%)
i686-gnu-1: 8561.7s -> 7935.8s (-7.3%)
dist-apple-various: 3973.9s -> 4260.9s (+7.2%)

How to interpret the job duration changes?

Job durations can vary a lot, based on the actual runner instance
that executed the job, system noise, invalidated caches, etc. The table above is provided
mostly for t-infra members, for simpler debugging of potential CI slow-downs.

rust-timer · 2025-12-29T06:14:35Z

Finished benchmarking commit (123588a): comparison URL.

Overall result: ❌ regressions - no action needed

@rustbot label: -perf-regression

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	1.7%	[1.7%, 1.7%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

This benchmark run did not return any relevant results for this metric.

Cycles

Results (secondary 0.3%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	3.6%	[3.6%, 3.6%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-3.0%	[-3.0%, -3.0%]	1
All ❌✅ (primary)	-	-	0

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 490.488s -> 483.839s (-1.36%)
Artifact size: 390.86 MiB -> 390.87 MiB (0.00%)

rustbot assigned cuviper Mar 2, 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 Mar 2, 2023

rustbot added T-libs-api Relevant to the library API team, which will review and decide on the PR/issue. and removed T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Mar 2, 2023

rustbot assigned joshtriplett and unassigned cuviper Mar 2, 2023

Coca162 mentioned this pull request Mar 2, 2023

Implementing flatten for Option<&Option<T>> and Option<&mut Option<T>> rust-lang/libs-team#186

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programmerjake reviewed Mar 3, 2023

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anden3 added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels May 14, 2023

Dylan-DPC added S-waiting-on-ACP Status: PR has an ACP and is waiting for the ACP to complete. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels May 20, 2023

rustbot assigned BurntSushi and unassigned joshtriplett Feb 11, 2024

bors added the S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. label Oct 2, 2024

dtolnay removed the S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. label Nov 3, 2024

dtolnay assigned dtolnay and unassigned BurntSushi Nov 3, 2024

Coca162 mentioned this pull request Nov 22, 2025

Tracking Issue for option_reference_flattening #149221

Open

4 tasks

Add flatten_{ref/mut} for Option<&Option<T>>/`Option<&mut Option<…

0e54845

…T>>`

Coca162 force-pushed the option_reference_flattening branch from 4dcfc5d to 0e54845 Compare November 22, 2025 17:31

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-ACP Status: PR has an ACP and is waiting for the ACP to complete. labels Dec 18, 2025

dtolnay approved these changes Dec 28, 2025

View reviewed changes

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 Dec 28, 2025

bors added the merged-by-bors This PR was explicitly merged by bors. label Dec 29, 2025

bors merged commit 123588a into rust-lang:main Dec 29, 2025
12 checks passed

rustbot added this to the 1.94.0 milestone Dec 29, 2025

Coca162 deleted the option_reference_flattening branch January 8, 2026 01:01

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Implement flatten for Option<&Option<T>> and Option<&mut Option<T>> #108671

Implement flatten for Option<&Option<T>> and Option<&mut Option<T>> #108671

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github-actions bot commented Dec 29, 2025

Test differences

Job duration changes

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rust-timer commented Dec 29, 2025

Overall result: ❌ regressions - no action needed

Instruction count

Max RSS (memory usage)

Cycles

Binary size

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Implement flatten for `Option<&Option<T>>` and `Option<&mut Option<T>>` #108671

Implement flatten for `Option<&Option<T>>` and `Option<&mut Option<T>>` #108671

Coca162 commented Mar 2, 2023 •

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