Simple Immutable Builder

Builder.php

<?php

abstract class Builder {

	abstract function build();

	function __call($name, $arguments)
	{
		if ( ! property_exists($this, $name))
		{
			throw new BadMethodCallException(sprintf('%s has no method "%s()"', __CLASS__, $name));
		}

		if (count($arguments) !== 1)
		{
			throw new InvalidArgumentException(sprintf('Only one argument must be provided to %s->%s()', __CLASS__, $name));
		}

		$new = clone $this;

		$new->$name = $arguments[0];

		return $new;
	}
}

PersonBuilder.php

<?php

final class PersonBuilder extends Builder {

  protected $name;
  
  protected $email;
  
  protected $age;
  
  function build()
  {
    // validate properties, exception if invalid
    // return a Person object
  }

}