Extends and private properties are in a boat…

gistfile1.php

<?php

namespace
{
	class abscisse
	{
		private $value;

		function __construct($value)
		{
			$this->value = $value;
		}
	}

	class ordinate extends abscisse
	{
	}

	class point
	{
		private
			$x,
			$y
		;

		function __construct(abscisse $x, ordinate $y)
		{
			$this->x = $x;
			$this->y = $y;
		}

		protected function abscisseAndOrdinateAreNeededByPoint(self $point)
		{
			$point->abscisseAndOrdinateAre($this->x, $this->y);

			return $this;
		}

		protected function abscisseAndOrdinateAre(abscisse $abscisse, ordinate $ordinate)
		{
			return $this;
		}
	}
}

namespace myPoint
{
	class displayer
	{
		function abscisseAndOrdinateAre(\abscisse $abscisse, \ordinate $ordinate)
		{
			var_dump($abscisse, $ordinate);

			return $this;
		}
	}

	class point extends \point
	{
		private
			$displayer
		;

		function displayerIs(displayer $displayer)
		{
			$this->displayer = $displayer;

			parent::abscisseAndOrdinateAreNeededByPoint($this);

			return $this;
		}

		protected function abscisseAndOrdinateAre(\abscisse $abscisse, \ordinate $ordinate)
		{
			$this->displayer->abscisseAndOrdinateAre($abscisse, $ordinate);

			return $this;
		}
	}

	(new point(new \abscisse(2), new \ordinate(3)))->displayerIs(new displayer);
}