ArrayUtils - Array flattener

array_utils.rb

require 'rspec'

# Utils for flattening an array recursively
# Usage: ArrayUtils.new(array_to_flatten).flatten
class ArrayUtils

  def initialize(array)
    raise 'Must be initialized with an array' unless array.kind_of? Array
    @array = array
  end

  def flatten
    recursive_flatten(@array, [])
  end

  private

    def recursive_flatten(array, flattened)
      array.each do |item|
        if item.kind_of? Array
          recursive_flatten(item, flattened)
        else
          flattened << item
        end
      end
      flattened
    end

end

# RSpec tests 
RSpec.describe ArrayUtils do
  it 'flattens [1, 2, 3, 4]' do
    expect(ArrayUtils.new([1, 2, 3, 4]).flatten).to eq [1, 2, 3, 4]
  end

  it 'flattens [1, [2], 3, 4]' do
    expect(ArrayUtils.new([1, [2], 3, 4]).flatten).to eq [1, 2, 3, 4]
  end

  it 'flattens [1, [2, 3], 4]' do
    expect(ArrayUtils.new([1, [2, 3], 4]).flatten).to eq [1, 2, 3, 4]
  end

  it 'flattens [1, [2, 3], 4]' do
    expect(ArrayUtils.new([1, [2, 3], 4]).flatten).to eq [1, 2, 3, 4]
  end

  it 'flattens [[1, [2, [3]], 4]]' do
    expect(ArrayUtils.new([[1, [2, [3]], 4]]).flatten).to eq [1, 2, 3, 4]
  end

  it 'flattens [[[1, [2, 3], 4]]]' do
    expect(ArrayUtils.new([[[1, [2, 3], 4]]]).flatten).to eq [1, 2, 3, 4]
  end

  it 'checks if array' do
    expect {
      ArrayUtils.new('1, 2, 3, 4')
    }.to raise_error('Must be initialized with an array')
  end

  it 'checks if not nil' do
    expect {
      ArrayUtils.new('')
    }.to raise_error('Must be initialized with an array')
  end

end