In your example, `has_my_thing` then has to be able to handle any possible input (even if it's just to say "I can't handle this input). Example: length of objec

In your example, `has_my_thing` then has to be able to handle any possible input (even if it's just to say "I can't handle this input). Example: length of objects/hashes, and length of arrays. And, sure, I guess you could `Array.has_my_thing(some_array)`... but that's just re-arranging the mixin structure behind `Array`. It only looks different until you start peaking under the hood. IMHO, sometimes you want a function because in your problem domain there's a universal (or universal enough) act/question/etc, and sometimes you want a member function because in your problem domain the act/question/etc only makes sense given some particular context.