null_pattern.php

<?php

# Implements a recursive null object pattern.
#
# Implemented as a trait so any object can make it's properties use
# the null pattern without resorting to inheritance.
#
# The goal is so you can pull data off a partially populated object
# without excessive existance checks.
trait NullPattern {

  # The real data we are wrapping. Since we continually return wrapped
  # objects if you ever want a unwrapped object the property can be
  # simply accessed
  public $__value__;

  function __call($name, $arguments) {
    $value = null;
    if( is_object($this->__value__) && method_exists($this->__value__, $name) ) {
      $value = call_user_func_array(array($this->__value__, $name), $arguments);
    }
    return new NullObject( $value );
  }

  function __get($name) {
    $value = null;
    if( is_object($this->__value__) && property_exists($this->__value__, $name) ) {
      $value = $this->__value__->$name;
    }
    return new NullObject( $value );
  }

  function  __set($name, $value) {
    if( is_object($this->__value__) )
      $this->__value__->$name = $value;
  }

  function __toString() {
    if( is_array($this->__value__) )
      return implode(', ', $this->__value__);
    else
      return (string) $this->__value__;
  }
}

# A general object that uses the NullPattern trait. Make it easy to
# turn any piece of data into something that behaves with the
# NullPattern.
class NullObject {
  use NullPattern;

  # Constructor to wrap a value in a NullObject object
  function __construct( $value = null ) {
    $this->__value__ = $value;
  }
}