PHP Pipeline，为什么要克隆对象？

Question

I was looking at some php code and stumbled on a pipeline script. In the method to add something to the pipeline:

public function pipe(callable $stage)
{
    $pipeline = clone $this;
    $pipeline->stages[] = $stage;
    return $pipeline;
}

The object is getting cloned, and returned. Could someone explain me the advantages of this approach, wouldn't the following code return the same results?

public function pipe(callable $stage)
{       
    $this->stages[] = $stage;
    return $this;
}

Answer 1

No, it won't return the same. Clone creates a copy of the object, which is sometimes the desired behaviour.

class WithoutClone {
    public $var = 5;

    public function pipe(callable $stage)
    {       
        $this->stages[] = $stage;
        return $this;
    }
}

$obj = new WithoutClone();
$pipe = $obj->pipe(...);
$obj->var = 10;
echo $pipe->var; // Will echo 10, since $pipe and $obj are the same object 
                 // (just another variable-name, but referencing to the same instance);

// ----

class Withlone {
    public $var = 5;

    public function pipe(callable $stage)
    {       
        $pipeline = clone $this;
        $pipeline->stages[] = $stage;
        return $pipeline;
    }
}

$obj = new WithClone();
$pipe = $obj->pipe(...);
$obj->var = 10;
echo $pipe->var; // Will echo 5, since pipe is a clone (different object);