[swift-evolution] [swift-evolution-announce] [Review] SE-0184: Unsafe[Mutable][Raw][Buffer]Pointer: add missing methods, adjust existing labels for clarity, and remove deallocation size

[Taylor Swift]

yeah, which is why I think the at:from: system is better than any subscript
alternative. I know everyone wants to use the square brackets but it just
doesn’t work very well for exactly the reasons you mentioned.

On Sat, Sep 30, 2017 at 6:07 PM, Dave Abrahams <dabrahams at apple.com> wrote:

>
>
> On Sep 29, 2017, at 4:03 PM, Taylor Swift <kelvin13ma at gmail.com> wrote:
>
>
>
> On Sep 29, 2017, at 5:56 PM, Dave Abrahams <dabrahams at apple.com> wrote:
>
>
>
> On Sep 29, 2017, at 3:48 PM, Taylor Swift <kelvin13ma at gmail.com> wrote:
>
>
>
> On Fri, Sep 29, 2017 at 4:13 PM, Andrew Trick <atrick at apple.com> wrote:
>
>>
>>
>> On Sep 29, 2017, at 1:23 PM, Taylor Swift <kelvin13ma at gmail.com> wrote:
>>
>> Instead of
>>>
>>>   buf.intialize(at: i, from: source)
>>>
>>> We want to force a more obvious idiom:
>>>
>>>   buf[i..<n].intialize(from: source)
>>>
>>>
>> The problem with subscript notation is we currently get the n argument
>> from the source argument. So what would really have to be written is
>>
>> buf[i ..< i + source.count].initialize(from: source)
>>
>> which is a lot more ugly and redundant. One option could be to decouple
>> the count parameter from the length of the source buffer, but that opens up
>> the whole can of worms in which length do we use? What happens if n - i is
>> less than or longer than source.count? If we enforce the precondition
>> that source.count == n - i, then this syntax seems horribly redundant.
>>
>>
>> Sorry, a better analogy would have been:
>>
>>  buf[i...].intialize(from: source)
>>
>> Whether you specify the slice’s end point depends on whether you want to
>> completely initialize that slice or whether you’re just filling up as much
>> of the buffer as you can. It also depends on whether `source` is also a
>> buffer (of known size) or some arbitrary Sequence.
>>
>> Otherwise, point  taken.
>>
>> -Andy
>>
>
> After thinking about this more, one-sided ranges might provide just the
> expressivity we need. What if:
>
> buf[offset...].initialize(from: source) // initializes source.count
> elements from source starting from offset
>
> buf[offset ..< endIndex].initialize(from: source) // initializes up to
> source.count elements from source starting from offset
>
>
> The one sided one does not give a full initialization guarantee. The two
> sided one guarantees the entire segment is initialized.
>
>
> In every other context, x[i...] is equivalent to x[i..<x.endIndex]
>
> I don't think breaking that precedent is a good idea.
>
> For move operations, the one sided one will fully deinitialize the source
> buffer while the two sided one will only deinitialize endIndex - offset
> elements.
>
>
> —
> -Dave
>
>
> well since people want to use subscript notation so much we need some way
> of expressing case 1. writing both bounds in the subscript seems to imply a
> full initialization (and thus partial movement) guarantee.
>
>
> Yes, I understood your reasoning.  Do you understand why I still don't
> want to proceed in that direction?
>
> —
> -Dave
>
>
>
>
>
>
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