First, my apologies to the readers. Something is chewing up my formatting and
indenting. I’m still trying to figure out a cause.
If we ignore implementation details and ownership it's pretty similar to what
we have with traits. In PHP, what would be the benefit of extensions over
traits? One thing that comes to my mind is that traits can be used by whatever
chooses to add it (back to ownership). Good one, but what else? If ownership is
the only concern then maybe a small addition to traits could achieve the same?
```
trait Foo
{
for Baz\Bar::class; // inverse of "use" to limit usage
}
class Bar
{
use Foo;
}
```
Brings conflict resolution for free; and I think it would be cheaper than yet
another class-like thing. Maybe also feels more php-ish since we already have
the trait concept?
If we ignore precise syntax and implementation, this is exactly the mental
model of my RFCs and implementations. It is applying a trait to an existing
class that you don’t control.
The similarities don’t end there. This is the same infrastructure as what is
used to implement this feature.
The reason I don’t feel the `trait … for` syntax is appropriate is because of
`$this`. In a function inside a typical trait, `$this` refers to an instance of
the trait. In an extension, `$this` refers to an instance of the class being
extended. Adding the `for` block to the trait changes the type of `$this` in
the entire trait. That is unintuitive and likely to introduce barriers to
understanding.
Holly
