Can PHP generators be cloned?

Question

In the PHP documentation it says that:

This flexibility does come at a cost, however: generators are forward-only iterators, and cannot be rewound once iteration has started. This also means that the same generator can't be iterated over multiple times: the generator will need to either be rebuilt by calling the generator function again, or cloned via the clone keyword. Documentation

However I tried writing a code that clones the generator object that I received from a method and I got an error specifying that a generator object cant be cloned:

class Course {
    private $students = array("avi" , "haim" , "maor" , "liran" , "yossi");

    function generateStudents() {
        foreach ($this->students as $student) {
            yield $student;
        }
    }
}

$ob = new Course();
$generator = $ob->generateStudents();

// Fatal error: Trying to clone an uncloneable object of class Generator
$generator2 = clone $generator;

?>

Answer 1

According to the RFC, generators cannot be cloned:

Generators cannot be cloned.

Support for cloning was included in the initial version, but removed in PHP 5.5 Beta 3 due to implementational difficulties, unclear semantics and no particularly convincing use cases.

It looks like the documentation reflects the initial version, and needs updating. There is a documentation bug raised to address this.

Also in the RFC, it refers to reasons why you might not want to reuse a generator:

Rewinding to some degree goes against the concept of generators, as they are mainly intended as one-time data sources that are not supposed to be iterated another time. On the other hand, most generators probably are rewindable and it might make sense to allow it. One could argue though that rewinding a generator is really bad practice (especially if the generator is doing some expensive calculation). Allowing it to rewind would look like it is a cheap operation, just like with arrays.