Example "Array#flatten" implementation

flatten.rb

def flatten(arg, results = [])
  if arg.is_a?(Array)
    arg.each do |val|
      flatten(val, results)
    end
  else
    results.push(arg)
  end

  return results
end

def assert(condition, message)
  raise message unless condition
end

assert(flatten([[1,2,[3]],4]) == [1, 2, 3, 4], 'arrays not equal')
assert(flatten([[1,2],[3, 4], 5, 6]) == [1, 2, 3, 4, 5, 6], 'arrays not equal')
assert(flatten([1, [2, [3, [4, [5, [6]]]]]]) == [1, 2, 3, 4, 5, 6], 'arrays not equal')