Probably needs an argument label since it's performing an explicit purpose, not
just a vanilla conversion initializer. So maybe
UnsafeRawBufferPointer.init(rebasing:)
Or since we have same-type constrained extensions now on master maybe you could
do it as a property:
extension RandomAccessSlice where Base == UnsafeRawBufferPointer {
var rebased: UnsafeRawBufferPointer {
return UnsafeRawBufferPointer(start: base.baseAddress, count: count)
}
}
(written by hand without a compiler so unlikely to be correct :)
> On Dec 8, 2016, at 18:07, Andrew Trick <atr...@apple.com> wrote:
>
>
>> On Dec 8, 2016, at 5:44 PM, Xiaodi Wu via swift-evolution
>> <swift-evolution@swift.org> wrote:
>>
>>> On Thu, Dec 8, 2016 at 6:53 PM, Ben Cohen via swift-evolution
>>> <swift-evolution@swift.org> wrote:
>>>
>>>> On Dec 8, 2016, at 4:35 PM, Jordan Rose via swift-evolution
>>>> <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).
>>
>> If this is indeed a requirement for Collection, then my vote would be for
>> Nate's option #1 and Andy's option #2, to give UnsafeRawBufferPointer a
>> Slice type that fulfills the requirement. It's the smallest change,
>> preserves the use of integer indices, and preserves what Andy stated as the
>> desired use case of making it easy for users to switch out code written for
>> [UInt8].
>
> Ok, but there needs to be an easy way in a nongeneric context to convert from
> a Slice<URBP> into an URBP (with normalized byte offsets).
>
> Does anyone object to adding an initializer for this? Any suggestions on
> naming? Do we need an argument label? etc?
>
> UnsafeRawBufferPointer(_ : Slice<UnsafeRawBufferPointer>)
>
> as in:
>
> let region = UnsafeRawBufferPointer(buffer[i..<j])
>
> -Andy
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