Disadvantages
Tagged pointers have some of the same difficulties as xor linked lists, although to a lesser extent. For example, not all debuggers will be able to properly follow tagged pointers; however, this is not an issue for a debugger that is designed with tagged pointers in mind.
The use of 0 to represent a null pointer does not suffer from these disadvantages: it is pervasive, and most programming languages treat 0 as a special null value. It has thoroughly proven its robustness. Usually when "tagged pointers" are spoken of, this common use is excluded.
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