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Date: Thu, 19 Mar 2015 23:23:45 +0000
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Subject: Re: [PHP-DEV] RFC - Array slice syntactic sugar
From: rowan.collins@gmail.com (Rowan Collins)

On 19/03/2015 20:49, Alex Bowers wrote:
> My proposal is something similar to Pythons slice, in PHP this would look
> like:
>
> $slided = $array[1:4]
>
> This will get the elements in positions 1,2,3,4. (1 through 4 inclusive),
> ignoring the actual key of the array. The result for an array will be an
> array with the keys preserved, in the same order.

While I can see the reasoning for not looking into the actual keys 
(which might not have a logically sliceable order), I think the syntax 
needs to be more distinct, because this seems a bit confusing:

$countdown = [ 5 => 'Five!', 4 => 'Four!', 3 => 'Three!', 2 => 'Two!', 1 
=> 'One!', 0 => 'Zero!' ]

$countdown[0]; // 'Zero!'
$countdown[0:0]; // ['Five!']
$countdown[0:][0] // 'Zero!'
$countdown[:0][0] // null - slice contains no key 0

The problem is that the slice access looks like an extension of key 
access, but is actually a new concept of positional element access. With 
a slight tweak to syntax, such as adding an @, we could make positional 
access available for non-slices as well:

reset($countdown); // Five! - a common way of getting the first element 
positionally
$countdown[@0]; // 'Five!'
$countdown[@1]; // 'Four!'
$countdown[@0:0] // ['Five!']
$countdown[@0:1] // ['Five!', 'Four!']
$countdown[@0:][@0] // 'Five!'
$countdown[@:0][@0] // 'Five!'


> A side addition, that may be considered is adding [-1] to get the last item
> in the array. But that is not a main part of this RFC.

This would actually be a really important addition for me, but only if I 
can do it on a non-slice, as above:

$countdown[-1]; // null - no such key
end($countdown); // 'Zero!'  - common way of getting last element
$countdown[@-1]; // 'Zero!' - positional access counting from the end
$countdown[@-2]; // 'One!' - fiddly to do in current PHP


I just wrote out all those examples and realised that it may not be 
possible to reuse @ in this context. Finding new symbols to use for 
syntax is hard. :(

Regards,

-- 
Rowan Collins
[IMSoP]