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Date: Thu, 31 Jul 2025 16:17:11 +0200
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Subject: Re: [PHP-DEV] [RFC] Optional Catch Block Body
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From: rob@bottled.codes ("Rob Landers")

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On Thu, Jul 31, 2025, at 15:32, Christian Schneider wrote:
> Am 31.07.2025 um 09:10 schrieb Rob Landers <rob@bottled.codes>:
> > I can see something like this being useful in niche applications. Fo=
r example, I have a proxy generation class that creates something like t=
his:
> >=20
> > public function remoteCall() {
> >   $this->operation =3D nameof($this->remoteCall(...));
> >   $this->arguments =3D func_get_args();
> >   throw new SpecialException();
> > }
> >=20
> > This SpecialException gets caught to let me know the application has=
 consumed the one-use proxy. Using it looks something like=20
> >=20
> > rpc(fn(RemoteObject $o) =3D> $o->remoteCall());
> >=20
> > which just provides type-safe rpc at the expense of some boilerplate.
> >=20
> > I also use empty exceptions to "jump" the stack when my framework kn=
ows there is nothing more to do until outside events happen. I think I c=
ould probably use fibers to do the same, but if the user is using a fibe=
r library; there is no guarantee they'll play nice together. This is tru=
e with exceptions as well, but the user has direct control over exceptio=
ns (do not catch Throwable, for instance).
>=20
> I'm not 100% sure I understood your examples but this smells like you =
are using exceptions for flow (or maybe state?) control which I'm not su=
re I would encourage.
>=20
> Regards,
> - Chris
>=20

It's explicitely to jump/unwind the stack -- PHP has no other way (other=
 than suspending a fiber or yielding a generator) to jump/unwind the sta=
ck to a given point. Fibers are the superior way here, but even then, th=
rowing from the fiber is still the best way to terminate it and force a =
GC of the stack there. This is basically using it as a longjmp (in C ter=
ms) which PHP doesn't have any other way to express. They're not used fo=
r flow control, or state. They merely force PHP to unwind the stack to a=
 known place (all possible side-effects have already been done and it is=
 either throw -- or wait for an external event, potentially forever -- w=
hich consumes memory and a thread).

=E2=80=94 Rob
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<!DOCTYPE html><html><head><title></title></head><body><div>On Thu, Jul =
31, 2025, at 15:32, Christian Schneider wrote:</div><blockquote type=3D"=
cite" id=3D"qt" style=3D""><div>Am 31.07.2025 um 09:10 schrieb Rob Lande=
rs &lt;<a href=3D"mailto:rob@bottled.codes">rob@bottled.codes</a>&gt;:</=
div><div>&gt; I can see something like this being useful in niche applic=
ations. For example, I have a proxy generation class that creates someth=
ing like this:</div><div>&gt;&nbsp;</div><div>&gt; public function remot=
eCall() {</div><div>&gt;&nbsp;&nbsp; $this-&gt;operation =3D nameof($thi=
s-&gt;remoteCall(...));</div><div>&gt;&nbsp;&nbsp; $this-&gt;arguments =3D=
 func_get_args();</div><div>&gt;&nbsp;&nbsp; throw new SpecialException(=
);</div><div>&gt; }</div><div>&gt;&nbsp;</div><div>&gt; This SpecialExce=
ption gets caught to let me know the application has consumed the one-us=
e proxy. Using it looks something like&nbsp;</div><div>&gt;&nbsp;</div><=
div>&gt; rpc(fn(RemoteObject $o) =3D&gt; $o-&gt;remoteCall());</div><div=
>&gt;&nbsp;</div><div>&gt; which just provides type-safe rpc at the expe=
nse of some boilerplate.</div><div>&gt;&nbsp;</div><div>&gt; I also use =
empty exceptions to "jump" the stack when my framework knows there is no=
thing more to do until outside events happen. I think I could probably u=
se fibers to do the same, but if the user is using a fiber library; ther=
e is no guarantee they'll play nice together. This is true with exceptio=
ns as well, but the user has direct control over exceptions (do not catc=
h Throwable, for instance).</div><div><br></div><div>I'm not 100% sure I=
 understood your examples but this smells like you are using exceptions =
for flow (or maybe state?) control which I'm not sure I would encourage.=
</div><div><br></div><div>Regards,</div><div>- Chris</div><div><br></div=
></blockquote><div><br></div><div>It's explicitely to jump/unwind the st=
ack -- PHP has no other way (other than suspending a fiber or yielding a=
 generator) to jump/unwind the stack to a given point. Fibers are the su=
perior way here, but even then, throwing from the fiber is still the bes=
t way to terminate it and force a GC of the stack there. This is basical=
ly using it as a longjmp (in C terms) which PHP doesn't have any other w=
ay to express. They're not used for flow control, or state. They merely =
force PHP to unwind the stack to a known place (all possible side-effect=
s have already been done and it is either throw -- or wait for an extern=
al event, potentially forever -- which consumes memory and a thread).<br=
></div><div><br></div><div id=3D"sig121229152">=E2=80=94 Rob</div></body=
></html>
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