Newsgroups: php.internals
Path: news.php.net
Xref: news.php.net php.internals:110939
MIME-Version: 1.0
Date: Sat, 11 Jul 2020 14:06:13 +0000
Message-ID: <CAJpLVh3VjCV4kR4n2EGnfYx8J6zQ7FafG7Q6kdbQ0HEMxZHMmw@mail.gmail.com>
To: internals@lists.php.net
Content-Type: text/plain; charset="UTF-8"
Subject: Possible RFC: UniqueInterface that throws exception at refcount > 1
From: olleharstedt@gmail.com (=?UTF-8?Q?Olle_H=C3=A4rstedt?=)

Dear internals,

I'd like to discuss the concept of ownership in PHP, from the point of
view of a new interface UniqueInterface (or SplUniqueInterface or
something), which will throw a UniqueException if refcount > 1.

Use-case: Mutable objects that cannot be shared (without (deep) cloning).

Rational: Immutable objects are considered "easier to reason about"
and generally more safe, and as a way to avoid
spooky-action-at-a-distance. I argue that mutability is totally fine
as long as it's not *being shared*. Currently, there's no way to
enforce this in PHP, *but* PHP has a refcounting GC which could do
this. This would be a more performant alternative than to build lots
of immutable objects using $obj->whereSomething('bla') constructs.

Cons: If PHP switches to tracing GC, it will be unusable.

What do you think? Should I write it down as an RFC? Implementation
should be straight-forward, assuming refcount is manipulated at a
single place in the source.

Regards
Olle