[swift-evolution] [Pitch] Normalize Slice Types for Unsafe Buffers
dabrahams at apple.com
Fri Dec 9 12:24:41 CST 2016
on Thu Dec 08 2016, Ben Cohen <ben_cohen-AT-apple.com> wrote:
>> On Dec 8, 2016, at 4:35 PM, Jordan Rose via swift-evolution
>> <swift-evolution at swift.org> wrote:
>> Um, Sequence doesn’t have a subscript (or indexes). Sequences
>> are single-pass. So if this is
> important, it needs to stay a Collection.
> Just because something fulfills one of the requirements of a
> Collection does not mean it should be
Um, it sorta does.
> It needs to tick all the boxes before its allowed to be
> But it’s still allowed to have subscripts (UnsafePointer has
> subscripting but isn’t a collection) or
> be multi-pass (strides are multiples but are only
> sequences). That’s OK
A sequence that is multipass can always be a collection, and
good reason to limit its expressivity by keeping it a sequence.
> In this case, yes it’s multi-pass, yes it has a subscript, but
> no it
> isn’t a collection because it doesn’t meet the requirements for
> slicing i.e. that indices of the slice be indices of the parent.
But it could. It's just a bug that we failed to get that right.
> (relatedly… it appears this requirement is documented on the
> Slice type rather than on Collection… which is a documentation
> bug we
> should fix).
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