Hi Andrea,
> On Jan 4, 2016, at 12:05, Andrea Faulds <[email protected]> wrote:
>
> Hi John,
>
> John Bafford wrote:
>> Happy New Year, everyone!
>>
>> I’d like to present the first new PHP RFC for this year, a proposal to add
>> functions to easily get the first, last, or an arbitrary key (and value) by
>> index from an array, taking advantage of PHP’s property that arrays are
>> ordered maps.
>>
>> RFC: https://wiki.php.net/rfc/array_key_first_last_index
>> PR: https://github.com/php/php-src/pull/347
>
> How often would such functions be useful? Perhaps they fill a gap, but I'm
> not sure if it's one that needs filling. array_key_first and array_key_last
> can already be accomplished in two or so lines of code (four if you make a
> function), and array_key_index can be implemented in a few lines with a
> foreach() loop and a counter.
array_key_first() and array_key_last() can’t be implemented in userspace and
maintain all three of fast, immutable, and doesn’t-look-weird.
The best you could do for array_key_first() is:
function array_key_first($arr) {
foreach($arr as $k => $v)
return $k;
return null;
}
Which already looks kind of weird. For array_key_last, your best bet is
function array_key_last($arr) {
$k = null;
foreach($arr as $k => $v)
;
//Rely on the fall-through of $k from the last iteration
return $k;
}
which looks even weirder
or
function array_key_last($arr) {
$keys = array_keys($arr);
if($cnt = count($keys))
return $keys[$cnt - 1];
return null;
}
Which adds the overhead of array_keys() iterating over the array and
duplicating *all* of the array’s keys just to retrieve one.
Any solution that uses reset() + key() or end() + key() mutates the array,
which means duplicating it if you pass it into a function. This takes a
non-trivial time if you have a large array.
> array_key_first and array_key_last seem mostly harmless, at least. I'm not
> sure the same can be said for array_key_index, since it has O(n) complexity.
> I worry that it might end up used by people who think it is more efficient
> than iterating through an array, even though it is not. I would rather we not
> include this specific function, and avoid potentially disguising the time
> complexity of key lookup, especially as I can't think of a good use-case for
> it. As for array_key_first and array_key_last, well, maybe they're useful, I
> have no strong opinion on them. They might be handy to get the first and last
> key of an array without moving the internal pointer, so who knows, maybe we
> should add them.
I’ll admit that array_key_index() could be easily abused. If you need to use it
more than a few times on a particular array, unless you’ve got a huge array and
need to keep memory use constrained, you’re probably better off just calling
array_keys() and using an index into the result. This would need to be included
in the documentation as a use case caveat, though it wouldn’t be surprising if
people ignored the warning and used it incorrectly anyway.
The reason array_key_index() is included in the RFC is because it kind of fell
out of the original implementation and since it’s kind of useful, for a limited
set of problems, I kept it in. It’s really more of a special-case tool with
(very) limited general use, but it is a substantial improvement over the
alternatives if you really do it need.
My primary goal with this RFC is array_key_first() and array_key_last(), so I
would not be against having array_key_index() be a separate voting choice, if
that would make people more comfortable.
> Thanks.
> --
> Andrea Faulds
> https://ajf.me/
-John
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