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To: Larry Garfield <larry@garfieldtech.com>
Subject: Re: [PHP-DEV] [RFC][Draft] Sealed Classes
From: mike@newclarity.net (Mike Schinkel)



> On Apr 27, 2021, at 7:00 PM, Larry Garfield <larry@garfieldtech.com> =
wrote:
>=20
> On Tue, Apr 27, 2021, at 5:48 PM, David Gebler wrote:
>> On Tue, Apr 27, 2021 at 11:23 PM Larry Garfield =
<larry@garfieldtech.com>
>> wrote:
>>=20
>> The two options to prevent such errors are:
>>>=20
>>> 1. Sealed classes.
>>> 2. Extend Enums into ADTs.
>>>=20
>>=20
>> Unless I've misunderstood your example, there is a third option which =
quite
>> possibly prevents the error in a nicer, easier to reason about, more
>> flexible pattern.
>>=20
>> class Perhaps extends Maybe implements OperatesOnTheValueInterface { =
... }
>=20
> If we were dealing with a service object in classic OOP (viz, OOP =
based on classes), then yes, turning the function into a method and =
using polymorphism would be the correct answer, rather than RTTI.
>=20
> However!  Classic OOP design patterns are not all that PHP supports, =
and that's a good thing.  The "class" construct, for better or worse, is =
the syntax for logic objects, value objects, data objects, and control =
flow objects (such as Maybe, Either, etc.), plus assorted other patterns =
that are not part of the classic OOP canon.  But they're still good and =
useful patterns, and often a better model than classic OOP "polymorph =
all the things" approaches.
>=20
> If we were designing PHP from scratch today, I'd argue for having =
separate language constructs for funcy-syntax-closures (which is what =
service objects are), product types (structs, value objects, all the =
same thing), and control flow types.  Many newer languages do =
differentiate those better.  That's not where we are, though, so we're =
stuck with class being the uber-syntax for anything even slightly =
interesting from a type perspective.

But, are we really, stuck? =20

You successfully introduced enumerations.  Why not also data types and =
control flow types?

Just asking for a "friend."


>  So be it, but it does lead to ample confusion about which use case =
you're talking about, especially when not everyone is familiar with all =
of the different, distinct use cases.
>=20
> See also: This thread. :-)
>=20
> Sealed classes are... not really useful at all for service object use =
cases.  They are useful for product type and control flow type use =
cases.
>=20
> --Larry Garfield
>=20
> --=20
> PHP Internals - PHP Runtime Development Mailing List
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>=20

-Mike=