PHP simple pipeline class

Pipe.php

<?php

namespace App\Utill;

class Pipe {

  /**
   * @var Any return value of last function
   */
  private $result = null;

  /**
   * Constructor
   * @param Callable function to pipe (optional)
   * @param Any argument of function
   * @return self
   */
  function __construct (Callable $function = null, $arg = null) 
  {
    if ($function != null) 
    {
      $this->result = $arg;
      $this->pipe($function);
    }

    return $this;
  }

  /**
   * Execute current function and save return value
   * @param Callable function
   * @return self
   */
  public function pipe (Callable $function)
  {
    if ($this->result != null) 
    {
      $this->result = $function($this->result);
    } 
    else 
    {
      $this->result = $function();
    }

    return $this;
  }

  /**
   * Get last return value
   * @return Any
   */
  public function getResult ()
  {
    return $this->result;
  }

  /**
   * Clean the result
   * @return self
   */
  public function end ()
  {
    $this->result = null;
    return $this;
  }

}