[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

[Dave Abrahams]

I’m sorry, but I think we disagree on the premise.  In my opinion the square brackets do exactly what we need them to do, and it’s not for the sake of anything other than consistency with the rest of the library and incidentally, reducing API complexity that I want to use them.

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> On Sep 30, 2017, at 6:04 PM, Taylor Swift <kelvin13ma at gmail.com> wrote:
> 
> okay, well until someone can come up with a subscript syntax that does what we need it to do, I’m inclined to view at:from: in the function parameter list as the clearest and most straightforward syntax. We shouldn’t use the square brackets for the sake of using square brackets.
> 
>> On Sat, Sep 30, 2017 at 6:51 PM, Dave Abrahams <dabrahams at apple.com> wrote:
>> I don't think I made any arguments that could be viewed as pointing out a problem with the slice approach, unless you take as given the idea that the slice approach should mean something novel and unprecedented. I don't see the whole/part implication that you see in the two notations, even though I understand why you want to read it that way, in particular because of the precedent I cited.
>> 
>>> On Sep 30, 2017, at 4:23 PM, Taylor Swift <kelvin13ma at gmail.com> wrote:
>>> 
>>> 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
>>>> 
>>>> 
>>>> 
>>>> 
>>>> 
>>> 
>> 
>> —
>> -Dave
>> 
>> 
>> 
>> 
>> 
> 
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