[swift-evolution] Range and ClosedRange

[Xiaodi Wu]

On Fri, Jan 13, 2017 at 2:05 PM, Max Moiseev via swift-evolution <
swift-evolution at swift.org> wrote:

> FWIW, the common RangeProtocol unifying both Range and ClosedRange existed
> for a while when the new collection indexing model was being implemented.
>
> Here is the commit removing it: https://github.com/apple/
> swift/pull/2108/commits/8e886a3bdded61e266678704a13edce00a4a8867
>
> Max
>

>From the commit: "The RangeProtocol was a very weak and fragile abstraction
because it didn't specify the interpretation of the endpoints.  To write a
non-trivial algorithm, one usually needed to consult that information."

As I argued (perhaps inarticulately) above, I think it may be worthwhile
revisiting the abstraction once conditional conformances become possible.
We can say more about the relationship between the endpoints of half-open
and closed _countable_ ranges than we can of uncountable ones.


>
> On Jan 12, 2017, at 12:11 PM, David Hart via swift-evolution <
> swift-evolution at swift.org> wrote:
>
> Hello,
>
> Since the release of Swift 3, I’ve seen quite a few people (me included)
> experience a lot of friction with the new types for representing ranges.
> I’ve seen people confused when writing an API that takes a Range as
> argument but then can’t pass in a ClosedRange. Sometimes this can be fixed
> because the API should be written against a more general protocol, but
> sometimes that’s not the case.
>
> Those new types definitely seem to cause more problems than they fixed
> (the Int.max problem). Has the Standard Library team put any thought into
> this?
>
> Regards,
> David.
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