I'm not a Ruby programmer so I have a simple question: Is it common to request whether an object implements a particular method before you make any sort of call? That seems considerably more fussy than strong typing of interfaces or even the type-hinting of interfaces that PHP has.

I can't help thinking a cleaner solution is the more traditional way: Create a subclass called NumberArray that can only hold numbers and has specific methods for operating on them. But I guess that might not be the "Ruby-way".