declaring interfaces using traits

[ju1ius]

Hi,

It would be nice to be able to declare interfaces using traits instead of structs, so that the following example would work:

#[php_interface]
pub trait Greeter {
  fn greet(&self) -> String;
}

#[php_class]
#[implements(Greeter)]
pub struct Hello(String);
#[php_impl]
impl Hello {
  pub fn __construct(subject: String) -> Self { Self(subject) }
}
#[php_impl]
impl Greeter for Hello {
  pub fn greet(&self) -> String { format!("Hello, {}!", self.0) }
}

<?php
$hello = new Hello('world');
assert($hello instanceof Greeter);
echo $hello->greet();

And it would be even nicer if the interface contract could work across the rust/php borders:

#[php_interface]
pub trait Greeter {
  fn greet(&self, subject: String) -> String;
}

#[php_class]
pub struct Greetable(String);
#[php_impl]
impl Greetable {
  pub fn __construct(name: String) {
    Self(name)
  }
  pub fn greeted(&self, greeter: impl Greeter) -> String {
    greeter.greet(self.0)
  }
}

<?php
$hello = new class implements Greeter {
  public function greet($subject: string): string {
    return "Hello, {$subject}";
  }
};
var_dump((new Greetable('world'))->greeted($hello)); // => "Hello, world!"

Thanks for the great work here btw !