> Am 16.10.2017 um 00:46 schrieb Xiaodi Wu <xiaodi...@gmail.com>:
>
> On Sun, Oct 15, 2017 at 2:39 PM, Kevin Nattinger <sw...@nattinger.net> wrote:
>>> […]
>>> Swift's Sequence protocol does not require the order of iteration to
>>> "convey any meaning"; it doesn't even require it to be deterministic.
>>>
>>
>> And that’s EXACTLY why none of the functions on Sequence should rely on the
>> order conveying meaning. `ElementsEqual` (for example) DOES rely on the
>> order of iteration conveying a meaning not required by the protocol, and
>> renaming it `lexicographicallyEquals` does not change that fact. Either
>> Sequence needs to require a meaningful order or `elementsEqual` should be
>> moved to a protocol that does.
>
> What's your basis for saying that `elementsEqual` requires orders of
> iteration that "convey a meaning"? It merely answers the question of whether
> iterating over `a` is substitutable for iterating over `b`, a question
> applicable to instances of any type which offers iterated access.
>
As Set has no intrinsic order of elements just imagine it was implemented to
have each iterator created on it to iterate in a random order. This would
satisfy the Sequence protocol (or rather its Iterable part hich should be split
off) and clearly show that the order is meaningless for Sets.
-Thorsten
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