A null object pattern implemented in PHP

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, $arguments) {
    if( is_object($this->__value__) && method_exists($this->__value__, $name) )
      return new NullObject(call_user_func_array(array($this->__value__, $name), $arguments));
    else
      return new NullObject();    
  }

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

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

  function __isset($name) {
    return is_object($this->__value__) && property_exists($this->__value__, $name);
  }

  function  __unset($name) {
    if( is_object($this->__value__) ) unset($this->__value__->$name);
  }

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

  # True if the raw value is not empty
  function present() {
    return !empty($this->__value__);
  }

  # If not present will return the given default value. If present
  # then returns the raw actual underlying value.
  function or_default($default) {
    if( $this->present() ) {
      return $this->__value__;
    } else {
      return $default;
    }
  }

  # Used to simulate array access when the wrapped object is a
  # non-asssociative array. So:
  #
  #   $list(5)
  #
  # functions like:
  #
  #   $list[5]
  #
  # Can also update an array in the same way:
  #
  #   $list(5, 'foo')
  #
  # works the same as:
  #
  #   $list[5] = 'foo'
  function __invoke($key) {
    if( !is_array($this->__value__) ) return new NullObject();
    if( func_num_args() > 1) $this->__value__[$key] = func_get_arg(1);
    if( array_key_exists($key, $this->__value__) )
      return new NullObject($this->__value__[$key]);
    else
      return new NullObject();
  }
}

# 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) {
    if( $value ) {
      if( is_assoc($value) ) $value = (object) $value;
      $this->__value__ = $value;
    }
  }
}

if( !function_exists('is_assoc') ) {
  # Copied from: http://www.php.net/manual/en/function.is-array.php#89332
  function is_assoc($v) {
    return is_array($v) && array_diff_key($v,array_keys(array_keys($v)));
  }
}