> On Jan 2, 2016, at 23:53, Dave Abrahams via swift-evolution
> <[email protected]> wrote:
>
>>
>> On Jan 2, 2016, at 11:26 PM, Kevin Ballard via swift-evolution
>> <[email protected]> wrote:
>>
>> On Sat, Jan 2, 2016, at 11:17 PM, Brent Royal-Gordon wrote:
>>>> `buffered` is no more problematic than `lazy` is. In fact, calling
>>>> `buffered` actually doesn't have any side-effects at all (it can avoid
>>>> fetching the first element until you call `first` on the result of
>>>> `buffered`).
>>>
>>> If `seq` is a single-pass sequence, then `seq.buffered.first` will consume
>>> an element from `seq`, even though you only accessed two properties. That's
>>> why I call it problematic.
>>>
>>> (If calling `buffered` somehow rendered the original sequence unusable—for
>>> instance, if we had some way to express that the `BufferedSequence` takes
>>> unique ownership of its base—this wouldn't bother me as much.)
>>
>> If `sequence` is a single-pass sequence, wrapping it in any other sequence
>> type and then doing anything with that other sequence type makes the
>> original sequence unusable (or rather, you can still use it but the elements
>> yielded from any further access to the original sequence can be completely
>> arbitrary).
>>
>> And for the record we already have precedent for the specific case of
>> `seq.prop1.prop2` destructively consuming the original sequence:
>> `seq.lazy.array`.
>
> Yes, and there are arguments for dropping “.array” as a property. The
> convention is that “conversions” (ill-defined, I know) use constructor
> syntax, and we are currently heading towards the elimination of "convenience”
> interfaces that duplicate functionality, so we might end up with Array(seq).
>
> All that said, single-pass Sequences are just weird in that they get mutated
> without calling any mutating methods on them; you mutate them by calling a
> mutating method on a separate generator instance. In other words, they
> fundamentally have reference semantics. There may be some better way to
> address this whole area, but we’ll have to go much deeper than merely poking
> at the question of a `.first` property.
Should "generate()" be a mutating method on SequenceType, then? And a
non-mutating one on CollectionType, obviously.
Jordan
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