Hmmm, so I have a handle class which allocates resources out of an internal pool, and creates objects that have a reference ID and uses the resource. Okay, now deep copy it.
The ID gets copied, the resource pointer gets... ? Copied? Or does there hypothetically exist a clone() virtual method for each superclass that would get invoked so the class could allocate another resource object, updating the reference ID? If it is a plain copy then when one of the two objects is deleted, the class is going to deallocate the resource associated with the reference ID and then you have problems when you go to use or delete the second copy. If it is not a plain copy, then can you guarantee there are additional resources available to allocate, and the operation is meaningful?
For example suppose I have a handle class that references a serial port object out of a modem pool. If you copy the same serial port then you get conflicts with resource use between the two objects. If you allocate a new modem out of the pool of modems, what if no modems were available, and is allocating a second modem what you really want to have happen in this situation?
If you deep-copy a handle that references a memory-mapped file, then should the file be duplicated?
I'm not convinced that providing an automatic deep copy method is a good idea in a language in which resources can be represented as well as pure data.