On the phpRiot blog, Quentin Zervaas has posted a quick tutorial about using the Iterator interface (part of the Standard PHP Library) together with Smarty to loop through some objects:

The PHP 5 Iterator interface is very useful for defining custom behaviour for looping over objects, however I just noticed that looping over such objects in Smarty will not work correctly. Smarty will in fact cast an object back to an array.

He includes code examples of his problem to illustrate and shows how he got around the problem - a getData() function he defined that just returns the array from the object.