how to return a copy of arguments but using CopyOnWrite scheme?

i'm truying to write a ext for php, personal usage in some case, my function modify the value and return for performance issue, i'd like to use CopyOnWrite scheme for the case returning without modify but how? _________________________________________________________________ The new MSN 8: smart spam protection and 2 months FREE* http://join.msn.com/?page=features/junkmail