Implement From<Cow<str>> for String and From<Cow<[T]>> for Vec<T>.
#37326
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Motivation: the `selectors` crate is generic over a string type, in order to support all of `String`, `string_cache::Atom`, and `gecko_string_cache::Atom`. Multiple trait bounds are used for the various operations done with these strings. One of these operations is creating a string (as efficiently as possible, re-using an existing memory allocation if possible) from `Cow<str>`. The `std::convert::From` trait seems natural for this, but the relevant implementation was missing before this PR. To work around this I’ve added a `FromCowStr` trait in `selectors`, but with trait coherence that means one of `selectors` or `string_cache` needs to depend on the other to implement this trait. Using a trait from `std` would solve this. The `Vec<T>` implementation is just added for consistency. I also tried a more general `impl<'a, O, B: ?Sized + ToOwned<Owned=O>> From<Cow<'a, B>> for O`, but (the compiler thinks?) it conflicts with `From<T> for T` the impl (after moving all of `collections::borrow` into `core::borrow` to work around trait coherence).
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Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @aturon (or someone else) soon. If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes. Please see the contribution instructions for more information. |
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@bors: r+ cc @rust-lang/libs, new In general we're pretty much always on board with adding various |
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📌 Commit 7e603d4 has been approved by |
alexcrichton
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@alexcrichton Wait, last time we regretted it, see #36685. |
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@bors: r- Indeed! Let's get a crater run this time. |
alexcrichton
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Crater report looks clean. @bors r=alexcrichton |
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📌 Commit 7e603d4 has been approved by |
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Implement `From<Cow<str>> for String` and `From<Cow<[T]>> for Vec<T>`. Motivation: the `selectors` crate is generic over a string type, in order to support all of `String`, `string_cache::Atom`, and `gecko_string_cache::Atom`. Multiple trait bounds are used for the various operations done with these strings. One of these operations is creating a string (as efficiently as possible, re-using an existing memory allocation if possible) from `Cow<str>`. The `std::convert::From` trait seems natural for this, but the relevant implementation was missing before this PR. To work around this I’ve added a `FromCowStr` trait in `selectors`, but with trait coherence that means one of `selectors` or `string_cache` needs to depend on the other to implement this trait. Using a trait from `std` would solve this. The `Vec<T>` implementation is just added for consistency. I also tried a more general `impl<'a, O, B: ?Sized + ToOwned<Owned=O>> From<Cow<'a, B>> for O`, but (the compiler thinks?) it conflicts with `From<T> for T` the impl (after moving all of `collections::borrow` into `core::borrow` to work around trait coherence).
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Are we generally OK with allocating |
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@SimonSapin Good point, thanks! |
Implement `From<Cow<str>> for String` and `From<Cow<[T]>> for Vec<T>`. Motivation: the `selectors` crate is generic over a string type, in order to support all of `String`, `string_cache::Atom`, and `gecko_string_cache::Atom`. Multiple trait bounds are used for the various operations done with these strings. One of these operations is creating a string (as efficiently as possible, re-using an existing memory allocation if possible) from `Cow<str>`. The `std::convert::From` trait seems natural for this, but the relevant implementation was missing before this PR. To work around this I’ve added a `FromCowStr` trait in `selectors`, but with trait coherence that means one of `selectors` or `string_cache` needs to depend on the other to implement this trait. Using a trait from `std` would solve this. The `Vec<T>` implementation is just added for consistency. I also tried a more general `impl<'a, O, B: ?Sized + ToOwned<Owned=O>> From<Cow<'a, B>> for O`, but (the compiler thinks?) it conflicts with `From<T> for T` the impl (after moving all of `collections::borrow` into `core::borrow` to work around trait coherence).
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I’ve just realized that I don’t strictly need a (I still think this PR is a good addition.) |
Motivation: the
selectorscrate is generic over a string type, in order to support all ofString,string_cache::Atom, andgecko_string_cache::Atom. Multiple trait bounds are used for the various operations done with these strings. One of these operations is creating a string (as efficiently as possible, re-using an existing memory allocation if possible) fromCow<str>.The
std::convert::Fromtrait seems natural for this, but the relevant implementation was missing before this PR. To work around this I’ve added aFromCowStrtrait inselectors, but with trait coherence that means one ofselectorsorstring_cacheneeds to depend on the other to implement this trait. Using a trait fromstdwould solve this.The
Vec<T>implementation is just added for consistency. I also tried a more generalimpl<'a, O, B: ?Sized + ToOwned<Owned=O>> From<Cow<'a, B>> for O, but (the compiler thinks?) it conflicts withFrom<T> for Tthe impl (after moving all ofcollections::borrowintocore::borrowto work around trait coherence).