> On Dec 8, 2016, at 4:54 PM, Jordan Rose <jordan_r...@apple.com> wrote:
>
>
>> On Dec 8, 2016, at 16:53, Ben Cohen <ben_co...@apple.com
>> <mailto:ben_co...@apple.com>> wrote:
>>
>>
>>> On Dec 8, 2016, at 4:35 PM, Jordan Rose via swift-evolution
>>> <swift-evolution@swift.org <mailto:swift-evolution@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 one. It needs to tick all the boxes before its allowed
>> to be elevated.
>>
>> 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
>>
>> 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.
>> (relatedly… it appears this requirement is documented on the concrete Slice
>> type rather than on Collection… which is a documentation bug we should fix).
>
> Ah, right, thank you. Retracted.
Let me restate, because I think Jordan's question was valid given my statement.
It would be *nice* for raw buffers to be Collection<UInt8> because they’re
meant to be a replacement for code that is typically written for [UInt8], and
anything you can do with an array that applies to raw buffers is covered by
Collection<UInt8>.
However, I don’t expect the raw buffer to be used in a generic context except
being passed to utilities that copy the bytes out. That will either be done by
directly iterating over the collection or invoking some other API that could
take a Sequence. The most important is probably Array.append(contentsOf:),
which is moving over to Sequence. However, we would also need to change
UnsafeRawBufferPointer(copyBytes:), NSData(replaceSubrange:), and whatever else
I haven't thought of. That's a small disadvantage to this solution.
I'm also a little concerned that Sequence is immutable, so generic code has no
way to copy bytes into the buffer.
My bigger concern is still that the range subscript’s inconsistent behavior may
still lead to bugs in practice in nongeneric code.
-Andy
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