lazy_load_when_required.php

<?php

/**
 * Lazy loads relationship if required
 *
 * @param \Eloquent $model
 * @param string $relationship
 *
 * @return object
 */
function load( &$model, $relationship )
{
	if ( !isset( $model->{$relationship} ) )
	{
		$model->load( $relationship );
	}

	return $model->{$relationship};
}

// usage example
$comments = load( $post, 'comments' );