> But not everything uses or needs CoW. In fact, the append operator is a useful method to copy something during a CoW function.

I think all of you have made it clear that it would indeed not be a good idea to only copy the data sometimes. It's just that I've encountered code using ~= where the "if(ar) ar~= else ar=" would yield some performance benefit. But I guess we'll have to optimize those cases manually.

Thanks for your points of view. They are appreciated!

L.