I wrote just such an object as an execise in learning the Tie interface. (Tie and Overload interact in strange ways.) However I have to say that the lack of an intuitive way to do this in Perl suprises me a little. Perhaps it has to do with how overloaded the various brackets are.
There is also Tie::CharArray which allows the same thing.
But frankly I hope that this is addressed in Perl 6...
You are not ready to use symrefs unless you already know why they are bad. -- tadmc (CLPM)