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One of the first things people often ask for when coming to Ruby is a ++ operator. The standard answer to that has always been that such a thing makes no sense in Ruby, since you don't want

1++

to turn literal ones into twos*1. But one thing one doesn't hear that often is that preincrement/predecrement operators can be simulated pretty straightforwardly with these semantics:

a = BoxedInteger.new(1)
a += 10
b = a   # => #<BoxedInteger:0xb7ddbd20 @value=11>
a.to_i  # => 11
++a  
a.to_i  # => 12
b.to_i  # => 12

I'll show an example involving arithmetic with boxed integers, but preincrement/decrement should never be used for that. I can only picture this being of use in some DSL*2.

This takes around 30 lines and it's a pretty interesting exercise, so you might want to try to write it on your own before I give my code. Here are some test cases that will tell you when you're done: