An implementation of the Merge Sort algorithm in Ruby

merge_sort.rb

class MergeSort
  # Sorts an array using the merge sort algorithm
  def sort(arr)
    length = arr.length
    if length > 1
      mid = (length/2).floor
      return merge(sort(arr[0..(mid - 1)]), sort(arr[mid..length]))
    else
      return arr
    end
  end

  private

  # Merges two array in sorted order
  def merge(left, right)
    if left.empty?
      return right
    elsif right.empty?
      return left
    elsif left.first < right.first
      return [left.first].concat(merge(left.drop(1), right))
    else
      return [right.first].concat(merge(left, right.drop(1)))
    end
  end
end

Tests for this class can be found here: https://gist.github.com/diegocasmo/cca7c07152c611dde2cd376081d428cc