Return type "self" in abstract PHP class

Question

Trying to make an abstract class to partially implement functionality of its' child classes and force a contract upon them required for this implementation, I use the following construct:

abstract class Parent {

    public static function fromDB(string $name = '') {
        $instance = new static();
        if (!empty($name)) {
            $instance->setName($name)->read();
        }
        return $instance;
    }

    public abstract function read();

    public abstract function setName(string $name): self;

}

Here PHP seems to understand that setName($name) returns an Object of type Parent, but PhpStorm indicates that read() can not be called on the result, which would have been the expected result.

Error Message: Referenced Method is not found in subject class.

I do not understand why this happens, and even suspect a bug in PHP or PhpStorm.

I've read up on Late static binding and the following questions which partially talk about this problem, but I couldn't figure out how to fix it:

• Question 1
• Question 2
• Late Static Binding Doc

Thank you for your time and help.

I'm trying to implement setName in child classes in a way so it is clear that the type of the returned Object is the one of the child:

public function setName(string $name = null): user {...}

which doesn't work with self return type and static is forbidden.

Answer 1

Your code sample looks fine in PhpStorm 2017.2 (currently in EAP stage) but shows warning in 2017.1.4.

Quite possibly it was fixed by WI-33991 or one of the related tickets.

---

You may get & try the 2017.2 EAP build at any time from here: http://confluence.jetbrains.com/display/PhpStorm/PhpStorm+Early+Access+Program

It comes with own 30-days license and can run in parallel to your current version (IDE-wide settings are stored in separate folders).

Answer 2

Try change to return static, static should indiciating you are returning the extending class, which may remove the error.

This is guess work but it's worth a shot.

public abstract function setName(string $name): static;

EDIT: Ok i dont think that will do, can you provide more information on the question? What is the purpose of read? fromDb? etc?

Answer 3

self will always refer to the class its in, never children classes. So when Parent says to return :self, it's expecting you to create a function that returns an instance of Parent. What you need to do is have your child class declare that it's doing that directly. Instead of declaring the child's setName will return :self (which is an instance of Child), we declare we're going to return our Parent class directly. PHP sees this as perfectly valid (Child is an instance of Parent after all)

We cannot use :static here because static is a reserved word in the class definitions

abstract class ParentTest {

    public static function fromDB(string $name = '') {
        $instance = new static();
        if (!empty($name)) {
            $instance->setName($name)->read();
        }
        return $instance;
    }

    public abstract function read();

    public abstract function setName(string $name): self;

}

class Child extends ParentTest {
    public function read() {

    }

    public function setName(string $name) :ParentTest {
        return $this;
    }
}

$child = new Child();

The above code runs without error

Answer 4

IMHO, there is an intelligent and SOLID approach to use interfaces. It is even required for libraries supposed to be used by 3rd-parties.

So, we just set the interface name as a type instead of 'self' in all parent classes and continue using 'self' for children.

<?php
interface EntityInterface 
{
    public function setName(string $name): EntityInterface;
}

abstract class ParentTest implements EntityInterface 
{

    public abstract function read();

    public abstract function setName(string $name): EntityInterface;

}

class Child extends ParentTest 
{
    
    private string $name = '';
    
    public function read(): string 
    {
        return $this->name;
    }

    public function setName(string $name): self 
    {
        $this->name = $name;
        return $this;
    }
}

$child = new Child();
echo $child->setName('hello')->read();