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Date: Fri, 21 Jun 2024 14:43:50 +0200
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Subject: Re: [PHP-DEV] [Early Feedback] Pattern matching
To: Andreas Hennings <andreas@dqxtech.net>
Cc: internals@lists.php.net
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From: landers.robert@gmail.com (Robert Landers)

On Fri, Jun 21, 2024 at 5:08=E2=80=AFAM Andreas Hennings <andreas@dqxtech.n=
et> wrote:
>
> > Ilija and I have been working on and off on an RFC for pattern matching=
 since the early work on Enumerations.
>
> I like what I see, a lot!
> One quick thought that came to my mind, regarding objects:
> Could we check method return values?
>
> if ($x is Countable { count(): 0 }) ...
> if ($p is Point { getX(): 3 }) ...
> if ($x is Stringable { __toString(): 'hello' }|'hello') ...
> while ($it is Iterator { valid(): true, current(): $value, next(): null }=
) ...
>
> Maybe it goes too far.
>
> For the variable binding, I noticed that we can overwrite the original va=
riable:
> $x is SomethingWrapper { something: $x }
> In this case the bool return is not really needed.
> For now this usage looks a bit unintuitive to me, but I might change
> my mind and grow to like it, not sure.
>
>
> For "weak mode" ~int, and also some other concepts, I notice that this
> RFC is ahead of the type system.
>
> E.g. should something like array<int> be added to the type system in
> the future, or do we leave the type system behind, and rely on the new
> "guards"?
> public array $values is array<int>
> OR
> public array<int> $values
>
> The concern here would be if in the future we plan to extend the type
> system in a way that is inconsistent or incompatible with the pattern
> matching system.
>
> --- Andreas

I'm always surprised why arrays can't keep track of their internal
types. Every time an item is added to the map, just chuck in the type
and a count, then if it is removed, decrement the counter, and if
zero, remove the type. Thus checking if an array is `array<int>`
should be a near O(1) operation. Memory usage might be an issue (a
couple bytes per type in the array), but not terrible.... but then
again, I've been digging into the type system quite a bit over the
last few months.