Writing the DebugSubject class

One common use case for Subject class is proxying all values and notifications from its source Observable.

In one of the preceding paragraphs, we wrote the PrintObserver class, which prints all values it receives. However, a more common situation is where we want to output values from an Observable while being able to chain it with another operator or observer. The Subject class exactly fits this use case, so we'll rewrite the preceding PrintObserver class and inherit Subject instead of AbstractObserver:

class DebugSubject extends Rx\Subject\Subject { 
  public function __construct($identifier=null, $maxLen=64){ 
    $this->identifier = $identifier; 
    $this->maxLen = $maxLen; 
  } 
  public function onCompleted() { 
    printf("%s%s onCompleted\n", $this->getTime(), $this->id());
    parent::onCompleted(); 
  }  
  public function onNext($val) { 
    $type = is_object($val) ? get_class($val) : gettype...