Building RESTful Web Services with PHP 7

Generator delegation

As functions can call each other, similarly a generator can also delegate to another generator. Here is how a generator delegates:

<?phpfunction gen(){    yield "yield 1 from gen1";    yield "yield 2 from gen1";    yield from gen2();}function gen2(){    yield "yield 1 from gen2";    yield "yield 2 from gen2";}foreach (gen() as $val){    echo $val, PHP_EOL;}/* above will result in output:yield 1 from gen1yield 2 from gen1yield 1 from gen2yield 2 from gen2 */

Here, gen2() is another generator being called in gen(), so a third yield in gen(), that is yield from gen2();, will transfer control to gen2(). So with that, it will start using yield from gen2().

Note that yield from is only usable with arrays, traversable, or generators. Using another ...