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Removal of exact capacity guarantee for Vec::with_capacity() is a breaking change #99385

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GoldsteinE opened this issue Jul 17, 2022 · 1 comment · Fixed by #135933
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Removal of exact capacity guarantee for Vec::with_capacity() is a breaking change #99385

GoldsteinE opened this issue Jul 17, 2022 · 1 comment · Fixed by #135933
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A-docs Area: Documentation for any part of the project, including the compiler, standard library, and tools T-libs-api Relevant to the library API team, which will review and decide on the PR/issue.

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@GoldsteinE
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Link #95614
Cc @jmaargh

Location

https://doc.rust-lang.org/nightly/std/vec/struct.Vec.html#method.with_capacity

Summary

Latest stable guarantees that Vec::with_capacity() always allocates exact capacity (and this is indeed the case, since RawVec discards any extra allocated capacity). #96173 removes this guarantee. I believe this to be a breaking change requiring some further investigation.
@GoldsteinE GoldsteinE added the A-docs Area: Documentation for any part of the project, including the compiler, standard library, and tools label Jul 17, 2022
@the8472
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the8472 commented Jul 17, 2022

Zulip discussion: https://rust-lang.zulipchat.com/#narrow/stream/219381-t-libs/topic/Vec.3A.3Awith_capacity.20promise

@workingjubilee workingjubilee mentioned this issue Jul 27, 2022
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@m-ou-se m-ou-se added T-libs-api Relevant to the library API team, which will review and decide on the PR/issue. I-libs-api-nominated Nominated for discussion during a libs-api team meeting. labels Oct 11, 2022
@m-ou-se m-ou-se mentioned this issue Oct 11, 2022
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@m-ou-se m-ou-se removed the I-libs-api-nominated Nominated for discussion during a libs-api team meeting. label Oct 18, 2022
@hkBst hkBst mentioned this issue Jan 23, 2025
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@bors bors closed this as completed in dc2b86f Feb 25, 2025
rust-timer added a commit to rust-lang-ci/rust that referenced this issue Feb 25, 2025
@rust-timer
Unrolled build for rust-lang#135933
aea7602 
Rollup merge of rust-lang#135933 - hkBst:patch-19, r=workingjubilee

Explain how Vec::with_capacity is faithful

This is a revival of rust-lang#99790 building on the prose of `@workingjubilee` and edits of `@jmaargh.` Closes rust-lang#99385.
github-actions bot pushed a commit to rust-lang/miri that referenced this issue Feb 26, 2025
@tgross35
Rollup merge of #135933 - hkBst:patch-19, r=workingjubilee
1241a6d 
Explain how Vec::with_capacity is faithful

This is a revival of rust-lang/rust#99790 building on the prose of `@workingjubilee` and edits of `@jmaargh.` Closes rust-lang/rust#99385.
github-actions bot pushed a commit to tautschnig/verify-rust-std that referenced this issue Mar 11, 2025
@tgross35
Rollup merge of rust-lang#135933 - hkBst:patch-19, r=workingjubilee
8eba2b6 
Explain how Vec::with_capacity is faithful

This is a revival of rust-lang#99790 building on the prose of `@workingjubilee` and edits of `@jmaargh.` Closes rust-lang#99385.
github-actions bot pushed a commit to tautschnig/verify-rust-std that referenced this issue Mar 11, 2025
@tgross35
Rollup merge of rust-lang#135933 - hkBst:patch-19, r=workingjubilee
3fc5093 
Explain how Vec::with_capacity is faithful

This is a revival of rust-lang#99790 building on the prose of `@workingjubilee` and edits of `@jmaargh.` Closes rust-lang#99385.
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