Asko Nõmm

Today I stumbled upon a little gotcha when writing traits in PHP. Namely, I wanted re-usable methods that would return self, so that I could chain method calls. However, I found that the Intelephense LSP (for VS Code, and Sublime Text) would not recognise the return type as the class that was using the trait, but instead as the trait.

So for the code of:

trait Foo {
    public function bar(): self {
        return $this;
    }
}

class Bar {
    use Foo;
}

(new Bar)->bar());

Intelephense would report that the return type of bar() was Foo, the trait, not Bar, the class. This is because the trait is not aware of the class that is using it, and so cannot return the correct type. Oddly enough returning static in the trait fixes the issue for Intelephense.

However, PHPStorm IDE doesn't seem to have a problem understanding the return type of self in traits, and resolves it as the union of all classes that are using the trait. I'm pretty sure this type of static analysis can be done with LSP's as well, so it just seems like a limitation in Intelephense.

Either way, if I want my code to be compatible with both, I'll have to use static instead of self.