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To: Chuck Adams <cja987@gmail.com>, =?iso-8859-1?Q?Olle_H=E4rstedt?=
	<olleharstedt@gmail.com>
CC: PHP internals <internals@lists.php.net>
Thread-Topic: [PHP-DEV] Possible RFC: UniqueInterface that throws exception at
 refcount > 1
Thread-Index: AQHWV4x7jXS7o3BhLEGSRfZHduTrhqkCcEqAgAAASmo=
Date: Sat, 11 Jul 2020 14:32:00 +0000
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Subject: Re: [PHP-DEV] Possible RFC: UniqueInterface that throws exception at
 refcount > 1
From: tysonandre775@hotmail.com (tyson andre)

Hi Olle=A0H=E4rstedt,=0A=
=0A=
> I'd like to discuss the concept of ownership in PHP, from the point of=0A=
> view of a new interface UniqueInterface (or SplUniqueInterface or=0A=
> something), which will throw a UniqueException if refcount > 1.=0A=
=0A=
It'd seem like it would cause a lot of places where UniqueException could b=
e thrown unexpectedly.=0A=
Additionally, inspecting the stack trace of an exception would also increme=
nt the refcount,=0A=
causing yet another exception.=0A=
=0A=
```=0A=
<?php=0A=
class UniqueObject{}=0A=
function test(UniqueObject $x) {=0A=
=A0 =A0 // ...=0A=
=A0 =A0 // handle some edge case=0A=
=0A=
=A0 =A0 // $trace includes an array with a reference to $x at $trace[0]['ar=
gs'][0],=0A=
=A0 =A0 // increasing the refcount to 2, throwing.=0A=
=A0 =A0 //=0A=
=A0 =A0 // Error handlers and issue handlers would also have this issues,=
=0A=
=A0 =A0 // as well as Throwable->getTrace()=0A=
=A0 =A0 $trace =3D debug_backtrace();=0A=
=A0 =A0 var_dump($trace);=0A=
}=0A=
test(new UniqueObject());=0A=
```=0A=
=0A=
> Implementation should be straight-forward, assuming refcount is manipulat=
ed at a=0A=
> single place in the source.=0A=
=0A=
This would also introduce some performance overhead if every function that =
incremented the reference count of a value=0A=
now had to check if objects implemented that interface. I'd assume it would=
 be significant.=0A=
=0A=
This is something that makes more sense in compiled languages like rust tha=
t can enforce uniqueness at compile time,=0A=
and the dynamic nature of php makes that less practical.=0A=
=0A=
- Tyson=0A=