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Date: Mon, 31 Oct 2016 12:07:13 -0600
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To: Larry Garfield <larry@garfieldtech.com>
Cc: internals <internals@lists.php.net>
Content-Type: text/plain; charset=UTF-8
Subject: Re: [PHP-DEV] Allow Iterator to be used with current, next, reset,
 key functions
From: levim@php.net (Levi Morrison)

On Mon, Oct 31, 2016 at 11:57 AM, Levi Morrison <levim@php.net> wrote:
> On Mon, Oct 31, 2016 at 11:27 AM, Larry Garfield <larry@garfieldtech.com> wrote:
>> On 10/31/2016 11:26 AM, Alice Wonder wrote:
>>>
>>> On 10/30/2016 10:19 AM, Rowan Collins wrote:
>>>
>>>>
>>>> - deprecate reset(), end(), each(), and key()
>>>> - introduce array_first(), array_last(), array_first_key() and
>>>> array_last_key()
>>>> - document replacements for whatever other use cases we can find
>>>> examples of
>>>>
>>>
>>> As a user I certainly like those names better. Semantic function names are
>>> a definite win in my view.
>>
>>
>>
>> Question: Now that we have "iterable" as a type, should we be adding more
>> array-specific functions or should such operations be designed, and named,
>> to operate on any iterable?  (first(), first_key(), etc.)
>
> At least for last and last-key I do not think we should make them work
> with any iterable. My reasoning is that we do not want to consume the
> iterator for them because many iterators are not rewindable (such as
> generators). The first and first-key routines should generally work
> because `rewind(); valid(); current(); rewind();` doesn't contain a
> `next()` call.
>
> Rewinding without iterating works for generators: https://3v4l.org/O7ZKO
> Rewinding after a next() call: https://3v4l.org/QI434

Additionally consuming the iterator would be an algorithmic complexity
of O(n) whereas for an array would just be O(1). So not only is it
annoying that the iterator is consumed and can't be guaranteed to be
rewound it is also costly.

The first and first-key routines do not have these issues.