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Date: Fri, 23 Dec 2022 14:29:07 +0100
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Subject: Re: [PHP-DEV] Methods which auto-return the class instance
From: claude.pache@gmail.com (Claude Pache)

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> Le 23 d=C3=A9c. 2022 =C3=A0 13:46, joke2k <joke2k@gmail.com> a =C3=A9cri=
t :
>=20
> On Fri, 23 Dec 2022, 09:33 Claude Pache, <claude.pache@gmail.com =
<mailto:claude.pache@gmail.com>> wrote:
>> It is very common for fluent class methods to have a verbose `return
>> $this;` ending in their body.
>> But If you have declared `self` as return type into a non-static =
class
>> method you have only two options to return:
>>=20
>> - the $this object
>> - another instance of the same class or subclass
>>=20
>> ... in order to avoid a return type error.
>=20
> It is still two options, and it is not clear in general which one to =
pick. You could also say that, if you have `object` as return type, =
there are two options to avoid a return type error: either return the =
`$this` object, or return another object.
>=20
> Yes but declaring `self` is more strict than `object`.=20
> And talking about the word itself... Declaring to return (your-)`self` =
but you could return someone-else of the same type as you.=20
> But it is ok, it refers to the class name not the instance. just =
semantic.
>=20


It is not about being less or more restricted, it is about being plainly =
ambiguous.

```php
class Point {
   =20
    public function __construct(
        protected float $x
      , protected float $y
    ) { }
   =20
    public function withY(float $y): static {
        $newPoint =3D clone $this;
        $newPoint->y =3D $y;
        // oops, forgot =E2=80=9Creturn $newPoint;=E2=80=9D
    }
}
```

With implicit behaviours (at least when there is more than one option), =
such sort of bugs become less apparent at runtime. Therefore, implicit =
behaviour ought to be avoided if possible.

=E2=80=94Claude


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