[swift-evolution] [swift-evolution-announce] [Returned for revision] SE-0089: Renaming String.init<T>(_: T)

Chris Lattner clattner at apple.com
Sat May 28 15:08:25 CDT 2016

On May 26, 2016, at 9:40 PM, Austin Zheng via swift-evolution <swift-evolution at swift.org> wrote:
>> Some remaining open questions:
>> - Exactly what types should conform to ValuePreservingStringConvertible.  It seems clear that integer, floating point types, and Character can and should conform.  What other types should?
> Like Brent mentioned, there are some types that are natural candidates, including Foundation types whose conformance could go into the overlays. NSURL, NSUUID, NSIndexPath. NSData is a borderline candidate, and probably not a good fit in the end (what encoding to use? what happens if you get the .description of a 100 MB NSData? etc). Same with NSDate. Maybe some of the CGStructs, although maybe the fact that CGFloat differs between platforms will sink that idea.

Yes, there definitely are Foundation types that could adopt this.  However, we don’t have a swift-evolution process at the moment to propose Foundation API extensions, so these would have to go through bugreporter.apple.com.

>> - Do we need the ValuePreservingStringConvertible at all, or is the existing CustomStringConvertible enough?  We already have a few protocols for handling string convertibility, it would be great to avoid adding another one.
> This is a good question.
> Since a ValuePreservingStringConvertible is, by definition, a type that can be represented as a string in a lossless and unambiguous manner, would it be worth requiring a reverse conversion in the form of a failable initializer taking a string? Some of the proposed ValuePreservingStringConvertible types already have such functionality today. It would give the protocol a little more of a reason to exist, as well as encouraging proper conformance.

Yes, this would be really great.  Perhaps obvious, but this could/should be expressed an initializer requirement in ValuePreservingStringConvertible.

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