RFC: Implement CowUtils on Cow<str> itself to enable chaining #5
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Chaining multiple calls to `CowUtils` methods will currently yield results tied to temporary lifetimes because intermediate `Cow<'s, str>` will be borrowed as `&'a str` via `&'a Cow<'s, str>` thereby loosing the original lifetime `'s`. By implementing `CowUtils` for `Cow<str>` we can chain the source lifetime through the calls at the cost of returning an owned `Cow::Owned(String)` instead of a borrow `&'a str` if a previous operation modified the source value, i.e. the calls in a chain will either all borrow or stop to completey at some point. Another cost is that to handle short-lived references to owned values, the trait itself must be extended to require a `Pattern` impl for any lifetime, not just the given source lifetime. I don't think this is usually an issue, but it does require a HRTB and is really only necessary for chaining.
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Chaining multiple calls to
CowUtilsmethods will currently yield results tied to temporary lifetimes because intermediateCow<'s, str>will be borrowed as&'a strvia&'a Cow<'s, str>thereby loosing the original lifetime's.By implementing
CowUtilsforCow<str>we can chain the source lifetime through the calls at the cost of returning an ownedCow::Owned(String)instead of a borrow&'a strif a previous operation modified the source value, i.e. the calls in a chain will either all borrow or stop to completey at some point.Another cost is that to handle short-lived references to owned values, the trait itself must be extended to require a
Patternimpl for any lifetime, not just the given source lifetime. I don't think this is usually an issue, but it does require a HRTB and is really only necessary for chaining.So in the end, I am not completely sure whether the design changes proposed here are really worth it, hence the RFC marker.