Recursive binary search

binary_search.rb

def search(array, number) #array must be sorted
  pivot = array.size / 2
  return pivot if array[pivot] == number
  if array[pivot] > number #Search on the left
    return search array.slice 0, pivot, number
  else #Search on the right
    return search array.slice pivot, array.size - pivot
  end
end

Ignoring the case where the number is not found for didactic purposes.