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Date: Sat, 22 Jun 2024 20:34:31 +0200
Message-ID: <CAPzBOBOwAbR=3cbyQxgYbnBEGcoJbkReOYVTsrd0ojBbZbf=ng@mail.gmail.com>
Subject: Re: [PHP-DEV] [Early Feedback] Pattern matching
To: "Rowan Tommins [IMSoP]" <imsop.php@rwec.co.uk>
Cc: internals@lists.php.net
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From: landers.robert@gmail.com (Robert Landers)

On Sat, Jun 22, 2024 at 8:04=E2=80=AFPM Rowan Tommins [IMSoP]
<imsop.php@rwec.co.uk> wrote:
>
> On 21/06/2024 19:29, Larry Garfield wrote:
>
> Valid points.  The line between validation and casting is a bit squishy,
>  as some casts can be forced (eg, string to int gives 0 sometimes), and
> others just cannot (casting to an object).  So would $a as
> array<~int> be casting, validating, or both?
>
>
> I think my concern is that both "x is T" and "x as T" read naturally as *=
expressions*, where their main purpose is to evaluate to a result, and side=
-effects are exceptional.
>
> From that point of view, we can give intuitive meaning to the following:
>
> - $foo is int =3D> boolean; is $foo of type int?
> - $foo is ~int =3D> boolean; can $foo be "safely" cast to int?
> - $foo as ~int =3D> int; cast $foo to int (unless unsafe)
>
> But then what does this mean?
>
> - $foo as int =3D> int; cast $foo to int if it's already an int !?

I've brought this up before, but I mostly see "as" being useful for
static analysis. That's what I've mostly used it for C#, anyway.
Logically, you know the type, but due to one-thing-or-another you
can't "prove" the type is that type (such as foreach-arrays or dealing
with results from user-code callbacks in library code). I want to be
able to say "this is an int or else."

[snip]

Now ... that being said, I'm def not a fan of this "~" thing. It makes
no sense to me. Semantically, what is the difference between "123",
123, and 123.0 other than how the bits are arranged in memory? If it
can become an int -- regardless of how it is laid out in memory -- I
expect to end up with an int as long as it is an integer. I would find
it super annoying to have to fix that bug report with a single
character, just because someone returned 123.0 instead of 123 because
they rounded the number and I got the result from a callback.

Further ~ means bitwise-not, so when you start mixing in literals ...
what does it mean?

$y =3D $x as ~1|~float;

What is the value of $y? Is it the literal negative two, casted to the
literal one (int), or casted a float?