Re: Pre-RFC proposal: opt-in implicit interfaces / structural typing

On Fri, Nov 7, 2025 at 5:05 PM 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: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 > > 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-interfaces Regards, Pedro