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Date: Mon, 30 Mar 2026 09:58:03 +0200
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Subject: Re: [PHP-DEV] RFC proposal: Invokable interface
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From: rob@bottled.codes ("Rob Landers")

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On Mon, Mar 30, 2026, at 09:37, Rowan Tommins [IMSoP] wrote:
> On 30 March 2026 01:32:24 BST, Osama Aldemeery <aldemeery@gmail.com> w=
rote:
>=20
> >The only difference is that __toString() has a fixed signature, so
> >Stringable can enforce it through a normal interface declaration.
> >__invoke() doesn't
> >have a fixed signature, so Invokable uses an enforcement handler inst=
ead.
> >Different mechanism, same contract. The difference is caused by the
> >variable signature, not by any fundamental difference in what the int=
erface
> >represents.
>=20
> I think that is a very fundamental difference.
>=20
> Given $foo instanceof Stringable, the user knows they can write (strin=
g)$foo and the object will do something - that's already a pretty weak c=
ontract, in my eyes, but it is a contract.
>=20
> Given $foo instanceof Invokable, the user knows even less. They know t=
hey can invoke the object somehow, but there's a fair chance that $foo()=
 will fail because of mandatory parameters.
>=20
> Can you give an example where this very loose contract would be useful?
>=20
> Regards,
>=20
> Rowan Tommins
> [IMSoP]

I'd prefer if the interface forced an empty argument set. You can add ar=
guments so long as they're optional. But generally speaking, there is no=
 need for arguments on an invokable class -- that is what constructors a=
nd properties are for.

=E2=80=94 Rob
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<!DOCTYPE html><html><head><title></title></head><body><div>On Mon, Mar =
30, 2026, at 09:37, Rowan Tommins [IMSoP] wrote:</div><blockquote type=3D=
"cite" id=3D"qt" style=3D""><div>On 30 March 2026 01:32:24 BST, Osama Al=
demeery &lt;<a href=3D"mailto:aldemeery@gmail.com">aldemeery@gmail.com</=
a>&gt; wrote:</div><div><br></div><div>&gt;The only difference is that _=
_toString() has a fixed signature, so</div><div>&gt;Stringable can enfor=
ce it through a normal interface declaration.</div><div>&gt;__invoke() d=
oesn't</div><div>&gt;have a fixed signature, so Invokable uses an enforc=
ement handler instead.</div><div>&gt;Different mechanism, same contract.=
 The difference is caused by the</div><div>&gt;variable signature, not b=
y any fundamental difference in what the interface</div><div>&gt;represe=
nts.</div><div><br></div><div>I think that is a very fundamental differe=
nce.</div><div><br></div><div>Given $foo instanceof Stringable, the user=
 knows they can write (string)$foo and the object will do something - th=
at's already a pretty weak contract, in my eyes, but it is a contract.</=
div><div><br></div><div>Given $foo instanceof Invokable, the user knows =
even less. They know they can invoke the object somehow, but there's a f=
air chance that $foo() will fail because of mandatory parameters.</div><=
div><br></div><div>Can you give an example where this very loose contrac=
t would be useful?</div><div><br></div><div>Regards,</div><div><br></div=
><div>Rowan Tommins</div><div>[IMSoP]<br></div></blockquote><div><br></d=
iv><div>I'd prefer if the interface forced an empty argument set. You ca=
n add arguments so long as they're optional. But generally speaking, the=
re is no need for arguments on an invokable class -- that is what constr=
uctors and properties are for.</div><div><br></div><div id=3D"sig1212291=
52">=E2=80=94 Rob</div></body></html>
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