Override a generator method within a class

Question

I have a method within a class that yields a couple of values. When calling the parent::generator_function() the values are not yielded. How yield them

class Papa
{
    public function generator_function()
    {
        yield 1;
        yield 2;
        yield 3;
    }
}

class Child extends Papa
{
    public function generator_function()
    {
        parent::generator_function();
        yield 4;
    }

}

$child = new Child();
foreach ($child->generator_function() as $value) {
    echo "$value\n";
};

Answer 1

Simply calling parent::generator_function() gives you a generator, which you're doing nothing with. Within a generator you can delegate to another generator via yield from.

In PHP 7, generator delegation allows you to yield values from another generator, Traversable object, or array by using the yield from keyword. The outer generator will then yield all values from the inner generator, object, or array until that is no longer valid, after which execution will continue in the outer generator.

E.g.:

class Child extends Papa
{
    public function generator_function()
    {
        yield from parent::generator_function();
        yield 4;
    }

}