Code that flattens arbitrary nested array in ruby

Array.flatten implementation

# method: flatten_array
# arguments: an unflattened array, and output array, initially set to [].
# output: a flattened array, so that arbitrary nesting of arrays is removed.
# the method employs tail recursion. It loops over each element of the array.
# if the current element is not an array, it adds it to the array it is building for output.
# but if the current element is an array, then it will call itself recursively so that the next call can iterate over this array element and add items from it recursively.


def flatten_array(array, start=[])
  array.each do |elem|
    if elem.is_a? Array
      flatten_array(elem, start)
    else
      start << elem
    end
  end
  start
end

#a = [[6, 4, 5], [[1], [2, [7]], [8, 6]], 9, 10, "", ["", nil, false]]
#b = flatten_array(a, [])