[swift-evolution] Adding a new filter method which returns 2 arrays

[Arman Shan]

I definitely agree that this function should not replace the current filter function. We can give it a new name like "partition" or something.

Regarding the memory constraint: since both filter and partition methods will be provided, the developer may choose whether they prefer performance over memory fragmentation or not.

Or maybe at the end of the partition method, if one of the result arrays is significantly smaller than the other, we copy the data into a smaller array and then return.

> On Jan 15, 2016, at 2:22 PM, Dave via swift-evolution <swift-evolution at swift.org> wrote:
> 
> I’m not sure if it’s currently done this way… In theory, filter can allocate enough contiguous memory to store all the results up front, skip all the overhead of expanding an array, and if it doesn’t all get used, well not caring (as much) about memory fragmentation is (one reason) why we have a 64-bit address space. This would be harder to do (or necessarily double the storage requirements) if filter could return two arrays, either of which could potentially contain as many elements as the original array.
> 
> Which is not to say I’m against having this because it does sound handy, I just don’t want it instead of the current filter function.
> 
> - Dave Sweeris
> 
>> On Jan 15, 2016, at 09:59, Arman Shan via swift-evolution <swift-evolution at swift.org> wrote:
>> 
>> Yes. I was thinking we would just copy over the filter implementation, and it should only need a small modification to keep track of the items being filtered, and finally return 2 arrays.
>> 
>> 
>>> On Jan 15, 2016, at 12:11 PM, Developer <devteam.codafi at gmail.com> wrote:
>>> 
>>> If we're going to add a partition method, can the original filter be rewritten in terms of it?
>>> 
>>> ~Robert Widmann
>>> 
>>> 2016/01/15 12:07、Nate Birkholz via swift-evolution <swift-evolution at swift.org> のメッセージ:
>>> 
>>>> That seems like a solid idea.
>>>> 
>>>>> On Fri, Jan 15, 2016 at 8:02 AM, Arman Shanjani via swift-evolution <swift-evolution at swift.org> wrote:
>>>>> Hi,
>>>>> 
>>>>> I was wondering if we could add a new filter method to the stdlib, where instead of returning just one array, it returns a tuple of 2 arrays, one with items that the closure returned true for and one with items that the closure returned false for. What do you think?
>>>>> 
>>>>> Thank you,
>>>>> 
>>>>> Arman
>>>>> 
>>>>> 
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>>>> 
>>>> 
>>>> 
>>>> -- 
>>>> Nate Birkholz
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