Call backs to user function

I am having trouble figuring out whether PHP copies classes or uses references when passing them. I have a class, foo, that in its constructor creates an object cb of class string_callback. I then call methods in cb with $this as one of the parameters. Later, when cb tries to call a method in foo it doesn't set the instance variables properly. The code for both foo and string_callback is attached. Normally, a php script opens a text file for reading. Then an object of type foo is created by calling: $bar = new foo($fh); where $fh is the handle to the open file. When I do this the $bar->status is not sticking. I is always an empty string after a callback. If anyone can explain this problem, I would very much appreciate it. Thanks. Peter Bowen pzb@lightningcast.net