This comes up every now and again, and lots of frameworks implement their own versions. I'm thinking 
of submitting an RCR for something functionally equivalent to the following to be incorporated into 
the base library:

class String
   def starts?(aString)
     index(aString) == 0
   end

   def ends?(aString)
     rindex(aString) == length - aString.length
   end
end

Of course, the real implementation would have much better performance. The advantage of including 
something like this is that these common functions can be made both high-performance and readable.

Comments?