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Date: Fri, 7 Nov 2025 22:20:35 +0000
Message-ID: <CAJd4=YZZYhmwAaRR=_2XJ2GdFCfS+RAd_PaCDuOmkwBSv84w6A@mail.gmail.com>
Subject: Re: [PHP-DEV] Pre-RFC proposal: opt-in implicit interfaces /
 structural typing
To: Spencer Malone <malone.spencer@gmail.com>
Cc: internals@lists.php.net
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From: mail@pmmaga.net (=?UTF-8?Q?Pedro_Magalh=C3=A3es?=)

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On Fri, Nov 7, 2025 at 5:05=E2=80=AFPM Spencer Malone <malone.spencer@gmail=
.com>
wrote:

> 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:imp=
licit,
> 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 a=
re
> 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, addin=
g
> 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 _wh=
y_
> I want this.
>
> - Spencer
>
>
Hi Spencer,

A few years ago I had a go at it. In case it is useful in any way, you can
check it in
https://github.com/php/php-src/compare/master...pmmaga:php-src:implicit-int=
erfaces

Regards,
Pedro

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<div dir=3D"ltr"><div class=3D"gmail_quote gmail_quote_container"><div dir=
=3D"ltr" class=3D"gmail_attr">On Fri, Nov 7, 2025 at 5:05=E2=80=AFPM Spence=
r Malone &lt;<a href=3D"mailto:malone.spencer@gmail.com">malone.spencer@gma=
il.com</a>&gt; wrote:<br></div><blockquote class=3D"gmail_quote" style=3D"m=
argin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left=
:1ex"><div dir=3D"ltr"><div>Hey all! Long time browser, first=C2=A0time ema=
iler. I wanted to start a pre-RFC discussion on the proposal of opt-in impl=
icit interfaces / 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"https://github.com/php/php-src/compare/master...SpencerMalone:php-src:i=
mplicit" target=3D"_blank">https://github.com/php/php-src/compare/master...=
SpencerMalone:php-src:implicit</a>, and was curious if this was an idea tha=
t could get any traction as an RFC?</div><div><br></div><div>For those who =
don&#39;t want to open the link, it&#39;s essentially:<br><br>```</div><div=
>implicit interface Drawable {<br>=C2=A0 =C2=A0 public function draw(): voi=
d;<br>}<br><br>class Circle {<br>=C2=A0 =C2=A0 public function draw(): void=
 {<br>=C2=A0 =C2=A0 }<br>}</div><div><br></div><div>assert((new Circle()) i=
nstanceof Drawable); // This would be true</div><div>```</div><div><br></di=
v><div>There is some previous art around here in the form of...</div><div><=
br></div><div><a href=3D"https://wiki.php.net/rfc/protocol_type_hinting" ta=
rget=3D"_blank">https://wiki.php.net/rfc/protocol_type_hinting</a> - I coul=
dn&#39;t find any discussion on this other than reading that the author wit=
hdrew=C2=A0all their RFCs for unrelated reasons I think? Some of the core i=
deas 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 ca=
ll sites because I wanted to provide the ability for interface definers to =
keep their interfaces as explicit if they wanted, as well as... Well honest=
ly, adding angle brackets around objects feels like a syntax misstep since =
that pattern is very associated with generics in my mind. I could be convin=
ced of this though if that&#39;s the syntax people prefer.</div><div><br></=
div><div><a href=3D"https://externals.io/message/115554#115603" target=3D"_=
blank">https://externals.io/message/115554#115603</a> - Convinced me that o=
thers may want this as well, although again that proposed syntax ended up s=
tepping on the toes of attributes. I do think this does a good job of expla=
ining _why_ I want this.</div><div><br></div><div>- Spencer</div><div><br><=
/div></div></blockquote><div><br></div><div>Hi Spencer,</div><div><br></div=
><div>A few years=C2=A0ago I had a go at it. In case it is useful in any wa=
y, you can check it in=C2=A0<a href=3D"https://github.com/php/php-src/compa=
re/master...pmmaga:php-src:implicit-interfaces">https://github.com/php/php-=
src/compare/master...pmmaga:php-src:implicit-interfaces</a></div><div><br><=
/div><div>Regards,</div><div>Pedro</div></div></div>

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