为什么在打电话给父母时使用退货？

Question

I am learning OO PHP and I was experimenting with using a parent::method in a child class. I noticed i had to use an "extra" return for the output of the parent method to show up. Could someone explain me why this is?

This is the code I used and in the code I made a comment.

class ShopProduct {

    public $productnumber;

    public function __construct($productnumber) {
        $this->productnumber = $productnumber;
    }
    public function getSummary(){
        return $this->productnumber;
    }
}

class BookProduct extends ShopProduct {

    public function __construct($productnumber) {
        parent::__construct($productnumber);
    }
    public function getSummary() {
        return parent::getSummary(); // if i dont use return it doesnt work? why is that?
        // parent::getSummary(); is not enough it seems.
    }
}

$product = new BookProduct(11111);
echo $product->getSummary();
?>

Answer 1

public function getSummary() {
    return parent::getSummary(); // if i dont use return it doesnt work? why is that?
    // parent::getSummary(); is not enough it seems.
}

Replace parent::getSummary() with any other function or method call:

public function getSummary() {
    foo();
}

Of course you wouldn't expect getSummary to return anything in this case, right? Just because the method you're calling is parent::... doesn't change anything about this behaviour. It does not return automagically, because you may want to do something like this:

public function getSummary() {
    $summary = parent::getSummary();
    return "Book: $summary";
}

BTW, if the only thing your method does is call its parent, you can leave out the entire method. In other words, this:

class BookProduct extends ShopProduct {

    public function __construct($productnumber) {
        parent::__construct($productnumber);
    }
    public function getSummary() {
        return parent::getSummary();
    }
}

is exactly the same as this:

class BookProduct extends ShopProduct { }