Add a resource-reusing method to ToOwned
#41009
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Odd, that error didn't show up from |
That tidy lint landed recently, so your local git might not have it yet. |
frewsxcv
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cc @rust-lang/libs |
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☔ The latest upstream changes (presumably #41102) made this pull request unmergeable. Please resolve the merge conflicts. |
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Rebased; looks like it's applying cleanly again. |
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Seems like a reasonable addition to me! |
src/libcollections/borrow.rs
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| /// let mut v: Vec<i32> = Vec::new(); | ||
| /// [1, 2][..].clone_into(&mut v); | ||
| /// ``` | ||
| #[unstable(feature = "toowned_clone_into", issue = "123456789")] // FIXME |
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To remind me to put a tracking issue in. If this has a plausible chance of acceptance, I can go create a placeholder now and put a real number.
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Discussed at libs triage the conclusion was to merge! @scottmcm want to update the tracking issue and I'll r+? |
to_owned generalizes clone; this generalizes clone_from. Use to_owned to give it a default impl. Customize the impl for [T], str, and T:Clone. Use it in Cow::clone_from to reuse resources when cloning Owned into Owned.
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Added tracking issue #41263 and squashed down to a single commit. |
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📌 Commit 7ec27ae has been approved by |
Add a resource-reusing method to `ToOwned` `ToOwned::to_owned` generalizes `Clone::clone`, but `ToOwned` doesn't have an equivalent to `Clone::clone_from`. This PR adds such a method as `clone_into` under a new unstable feature `toowned_clone_into`. Analogous to `clone_from`, this has the obvious default implementation in terms of `to_owned`. I've updated the `libcollections` impls: for `T:Clone` it uses `clone_from`, for `[T]` I moved the code from `Vec::clone_from` and implemented that in terms of this, and for `str` it's a predictable implementation in terms of `[u8]`. Used it in `Cow::clone_from` to reuse resources when both are `Cow::Owned`, and added a test that `Cow<str>` thus keeps capacity in `clone_from` in that situation. The obvious question: is this the right place for the method? - It's here so it lives next to `to_owned`, making the default implementation reasonable, and avoiding another trait. But allowing method syntax forces a name like `clone_into`, rather than something more consistent like `owned_from`. - Another trait would allow `owned_from` and could support multiple owning types per borrow type. But it'd be another single-method trait that generalizes `Clone`, and I don't know how to give it a default impl in terms of `ToOwned::to_owned`, since a blanket would mean overlapping impls problems. I did it this way as it's simpler and many of the `Borrow`s/`AsRef`s don't make sense with `owned_from` anyway (`[T;1]:Borrow<[T]>`, `Arc<T>:Borrow<T>`, `String:AsRef<OsStr>`...). I'd be happy to re-do it the other way, though, if someone has a good solution for the default handling. (I can also update with `CStr`, `OsStr`, and `Path` once a direction is decided.)
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☀️ Test successful - status-appveyor, status-travis |
…crichton Override ToOwned::clone_into for Path and OsStr The only non-overridden one remaining is the CStr impl, which cannot be optimized as doing so would break CString's second invariant. Follow-up to 7ec27ae (PR rust-lang#41009). r? @alexcrichton
…crichton Override ToOwned::clone_into for Path and OsStr The only non-overridden one remaining is the CStr impl, which cannot be optimized as doing so would break CString's second invariant. Follow-up to 7ec27ae (PR rust-lang#41009). r? @alexcrichton
ToOwned::to_ownedgeneralizesClone::clone, butToOwneddoesn't have an equivalent toClone::clone_from. This PR adds such a method asclone_intounder a new unstable featuretoowned_clone_into.Analogous to
clone_from, this has the obvious default implementation in terms ofto_owned. I've updated thelibcollectionsimpls: forT:Cloneit usesclone_from, for[T]I moved the code fromVec::clone_fromand implemented that in terms of this, and forstrit's a predictable implementation in terms of[u8].Used it in
Cow::clone_fromto reuse resources when both areCow::Owned, and added a test thatCow<str>thus keeps capacity inclone_fromin that situation.The obvious question: is this the right place for the method?
to_owned, making the default implementation reasonable, and avoiding another trait. But allowing method syntax forces a name likeclone_into, rather than something more consistent likeowned_from.owned_fromand could support multiple owning types per borrow type. But it'd be another single-method trait that generalizesClone, and I don't know how to give it a default impl in terms ofToOwned::to_owned, since a blanket would mean overlapping impls problems.I did it this way as it's simpler and many of the
Borrows/AsRefs don't make sense withowned_fromanyway ([T;1]:Borrow<[T]>,Arc<T>:Borrow<T>,String:AsRef<OsStr>...). I'd be happy to re-do it the other way, though, if someone has a good solution for the default handling.(I can also update with
CStr,OsStr, andPathonce a direction is decided.)