[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]

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. For move
operations, the one sided one will fully deinitialize the source buffer
while the two sided one will only deinitialize endIndex - offset elements.
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