self type considered harmful

[widmogrod]

When using interface with self as return i.e. Functor new class require reimplementing.

class A implements Functor {
    public function map(callable $function): self {
    }
}

this code results in error

 Declaration of A::map(callable $function): A must be compatible with FunctionalPHP\FantasyLand\Functor::map(callable $function): FunctionalPHP\FantasyLand\Functor in (..)

To fix it, interface should have explicit return type

class A implements Functor {
    public function map(callable $function): Functor {
    }
}

[krtek4]

What about Apply and Chain ?

[widmogrod]

@krtek4 good catch.

[krtek4]

:+1: