Aspect-Oriented PHP logger

WithLogging.php

<?php
// This class impersonates other objects and logs what they do.

class WithLogging {
  // The parameter customMessage is a function that knows something about
  // callee and can give extra interesting information about its state.
  function __construct($callee, $customMessage = NULL) {
    $this->callee        = $callee;
    $this->customMessage = $customMessage ?: function($obj) { return ''; };
  }

  // All method invocations of WithLogging go through here, and are
  // forwarded to callee and logged appropriately.
  function __call($method, $args) {
    $fullName = get_class($this->callee) . "::{$method}";
    if(!method_exists($this->callee, $method)) {
      $trace = debug_backtrace();
      trigger_error("Call to undefined method $fullName() in " .
                    "{$trace[0]['file']} on line {$trace[0]['line']}",
                    E_USER_ERROR);
    }
    echo "$fullName(" . implode(', ', $args) . ")\n\t";
    $ret = call_user_func_array(array($this->callee, $method), $args); 
    echo call_user_func($this->customMessage, $this->callee) . "\n";
    return $ret;
  }

  protected $callee;
  protected $customMessage;
}
?>