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Date: Sun, 17 Mar 2024 16:46:23 +0000
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Subject: Re: [PHP-DEV] [Pre-RFC] Improve language coherence for the behaviour
 of offsets and containers
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From: imsop.php@rwec.co.uk ("Rowan Tommins [IMSoP]")

On 11/03/2024 12:52, Gina P. Banyard wrote:
> I would like to get some initial feedback on an RFC I've been working on for the last 5–6 months.
> The RFC attempts to explain, and most importantly, improve the semantics around $container[$offset] as PHP is currently widely inconsistent.
>
> [...]
>
> RFC: https://github.com/Girgias/php-rfcs/blob/master/container-offset-behaviour.md


Hi Gina,

I've just read through this thoroughly, and am simultaneously impressed 
with your investigation, and amazed at how many inconsistencies you found.


I think the proposed granular interfaces absolutely make sense, given 
the different uses people have for such offsets. My only hesitation is 
that if you want "everything", things become quite verbose:

class Foo implements DimensionFetchable, DimensionWritable, 
FetchAppendable, DimensionUnsettable { ... }

function 
bar(DimensionFetchable&DimensionWritable&FetchAppendable&DimensionUnsettable 
$container) { ... }

Unfortunately, I can't think of an easy solution to this without some 
form of type aliases.


As an experiment, I tried writing a variation of Python's "defaultdict" 
[1] using all the new hooks (without actually testing it against any 
implementation). Here's what I came up with: 
https://gist.github.com/IMSoP/fbd60c5379ccefcab6c5af25eacc259b

Most of it is straight-forward, but a couple of things stood out:

* Separating offsetFetch from offsetGet is really useful, because we can 
avoid "auto-vivifying" a key that's only been read, never updated. In 
other words, isset($foo['a']) can remain false after running 
var_dump($foo['a']), but $foo['a']++ should still work.

* The fetchAppend hook is quite confusing to implement, because it's 
used in a few subtly different scenarios. For instance, if it's actually 
$container[][$offset] = $value there is an implicit requirement that 
fetchAppend should return array|DimensionWritable, but presumably that 
has to be enforced after fetchAppend has returned. I'm not sure if 
there's anything that can be improved here; it probably just needs some 
examples in the user manual.

[1] 
https://docs.python.org/3/library/collections.html#collections.defaultdict


Over all, I think this is a really great proposal, and hope it proceeds 
smoothly.

Regards,

-- 
Rowan Tommins
[IMSoP]