In the process of writing some RSpec tests, I found it useful to be able to add arrays of numbers together as you would vectors.
Of course Ruby has a Vector class, but I was intrigued as to how I might implement such a thing and what extra utility I could provide; I came up with the following:

module Enumerable
def **(other)
zip(other.fill(0, other.size, size - other.size)).collect {|a| a.inject {|sum,e| sum+e}}
end
def vector_add *others
sums = nil
if block_given?
each do |e|
sums = sums.nil? ? yield(e) : sums ** yield(e)
end
else
sums = self
end
others.each do |other|
sums = sums.nil? ? other : sums ** other
end if not others.empty?
return sums
end
end

As you can see I have overridden the

`**`

(exponentiation) operator; not sure this is a great idea, that is perhaps violating some 'behavioral integrity', but it can always be changed or replaced.
Try running the above and following code (try pasting into IRB)...

puts [1,2,3] ** [4,5,6]
puts [1,2,3,4] ** [4,5,6]
puts [1,2,3].vector_add([4,5,6])
puts [1,2,3,4].vector_add {|e| [e*1, e*2, e*3, e*4]}
puts [1,2,3,4].vector_add([4,5,6]) {|e| [e*1, e*2, e*3, e*4]}

You should get something like the following:

5
7
9
5
7
9
4
5
7
9
10
20
30
40
14
25
36
40

I'm pretty pleased with that. Now, back to RSpec...