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Date: Fri, 7 Nov 2025 09:05:03 -0800
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Subject: [PHP-DEV] Pre-RFC proposal: opt-in implicit interfaces / structural typing
To: internals@lists.php.net
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From: malone.spencer@gmail.com (Spencer Malone)

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Hey all! Long time browser, first time emailer. I wanted to start a pre-RFC
discussion on the proposal of opt-in implicit interfaces / structural
typing / "golang style interfaces".

I have an early mostly working POC at
https://github.com/php/php-src/compare/master...SpencerMalone:php-src:implicit,
and was curious if this was an idea that could get any traction as an RFC?

For those who don't want to open the link, it's essentially:

```
implicit interface Drawable {
    public function draw(): void;
}

class Circle {
    public function draw(): void {
    }
}

assert((new Circle()) instanceof Drawable); // This would be true
```

There is some previous art around here in the form of...

https://wiki.php.net/rfc/protocol_type_hinting - I couldn't find any
discussion on this other than reading that the author withdrew all their
RFCs for unrelated reasons I think? Some of the core ideas here I think are
still relevant, although in my implementation I chose to use syntax that
adds a keyword onto the interface rather than at the call sites because I
wanted to provide the ability for interface definers to keep their
interfaces as explicit if they wanted, as well as... Well honestly, adding
angle brackets around objects feels like a syntax misstep since that
pattern is very associated with generics in my mind. I could be convinced
of this though if that's the syntax people prefer.

https://externals.io/message/115554#115603 - Convinced me that others may
want this as well, although again that proposed syntax ended up stepping on
the toes of attributes. I do think this does a good job of explaining _why_
I want this.

- Spencer

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<div dir=3D"ltr"><div>Hey all! Long time browser, first=C2=A0time emailer. =
I wanted to start a pre-RFC discussion on the proposal of opt-in implicit i=
nterfaces / structural typing / &quot;golang style interfaces&quot;.</div><=
div><br></div><div>I have an early mostly working POC at=C2=A0<a href=3D"ht=
tps://github.com/php/php-src/compare/master...SpencerMalone:php-src:implici=
t">https://github.com/php/php-src/compare/master...SpencerMalone:php-src:im=
plicit</a>, and was curious if this was an idea that could get any traction=
 as an RFC?</div><div><br></div><div>For those who don&#39;t want to open t=
he link, it&#39;s essentially:<br><br>```</div><div>implicit interface Draw=
able {<br>=C2=A0 =C2=A0 public function draw(): void;<br>}<br><br>class Cir=
cle {<br>=C2=A0 =C2=A0 public function draw(): void {<br>=C2=A0 =C2=A0 }<br=
>}</div><div><br></div><div>assert((new Circle()) instanceof Drawable); // =
This would be true</div><div>```</div><div><br></div><div>There is some pre=
vious art around here in the form of...</div><div><br></div><div><a href=3D=
"https://wiki.php.net/rfc/protocol_type_hinting">https://wiki.php.net/rfc/p=
rotocol_type_hinting</a> - I couldn&#39;t find any discussion on this other=
 than reading that the author withdrew=C2=A0all their RFCs for unrelated re=
asons I think? Some of the core ideas here I think are still relevant, alth=
ough in my implementation I chose to use syntax that adds a keyword onto th=
e interface rather than at the call sites because I wanted to provide the a=
bility for interface definers to keep their interfaces as explicit if they =
wanted, as well as... Well honestly, adding angle brackets around objects f=
eels like a syntax misstep since that pattern is very associated with gener=
ics in my mind. I could be convinced of this though if that&#39;s the synta=
x people prefer.</div><div><br></div><div><a href=3D"https://externals.io/m=
essage/115554#115603">https://externals.io/message/115554#115603</a> - Conv=
inced me that others may want this as well, although again that proposed sy=
ntax ended up stepping on the toes of attributes. I do think this does a go=
od job of explaining _why_ I want this.</div><div><br></div><div>- Spencer<=
/div><div><br></div></div>

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