Instructions

Attempting to implement a mergesort algorithm, pry exited with the included error message. The corresponding algorithm is attached also.

mergeSort.rb

class MergeSort
  def initialize(array_to_sort)
    @array_to_sort = array_to_sort
  end

  def recursive_divisor_and_collector(array_to_sort)
    @array_to_sort if @array_to_sort.size <= 1
    array_divided = @array_to_sort.slice!( (@array_to_sort.size/2).round, @array_to_sort.length )
    left_unsorted_array = recursive_divisor_and_collector(@array_to_sort)
    right_unsorted_array = recursive_divisor_and_collector(array_divided)
    sorted_array = merge(left_unsorted_array, right_unsorted_array)
  end

  def self.merge(left_unsorted_array, right_unsorted_array)
    sorted_array = []
    until left_unsorted_array || right_unsorted_array <= 1
      if left_unsorted_array[0] <= right_unsorted_array[0]
        sorted_array << left_unsorted_array[0]
      elsif right_unsorted_array[0] <= left_unsorted_array[0]
        sorted_array << right_unsorted_array[0]
      end
    end
    sorted_array + left_unsorted_array + right_unsorted_array
  end
end

terminal_output

2.1.0 (main):0 > load 'mergeSort.rb'
=> true
2.1.0 (main):0 > merging = MergeSort.new([4,7,23,9,0,3,2,16,5])
=> #<MergeSort:0x007f9e4b3b0f60 @array_to_sort=[4, 7, 23, 9, 0, 3, 2, 16, 5]>
2.1.0 (main):0 > merging.recursive_divisor_and_collector(@array_to_sort)
/Users/gringocl/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/pry-0.9.12.4/lib/pry/pry_instance.rb:523:in `attr_accessor': can't modify frozen Class (RuntimeError)
        from /Users/gringocl/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/pry-0.9.12.4/lib/pry/pry_instance.rb:523:in `singleton class'
        from /Users/gringocl/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/pry-0.9.12.4/lib/pry/pry_instance.rb:522:in `last_exception='
        from /Users/gringocl/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/pry-0.9.12.4/lib/pry/pry_instance.rb:280:in `rescue in re'
        from /Users/gringocl/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/pry-0.9.12.4/lib/pry/pry_instance.rb:270:in `re'
        from /Users/gringocl/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/pry-0.9.12.4/lib/pry/pry_instance.rb:254:in `rep'
        from /Users/gringocl/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/pry-0.9.12.4/lib/pry/pry_instance.rb:234:in `block (3 levels) in repl'
        from /Users/gringocl/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/pry-0.9.12.4/lib/pry/pry_instance.rb:232:in `loop'
        from /Users/gringocl/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/pry-0.9.12.4/lib/pry/pry_instance.rb:232:in `block (2 levels) in repl'
        from /Users/gringocl/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/pry-0.9.12.4/lib/pry/pry_instance.rb:231:in `catch'
        from /Users/gringocl/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/pry-0.9.12.4/lib/pry/pry_instance.rb:231:in `block in repl'
        from /Users/gringocl/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/pry-0.9.12.4/lib/pry/pry_instance.rb:230:in `catch'
        from /Users/gringocl/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/pry-0.9.12.4/lib/pry/pry_instance.rb:230:in `repl'
        from /Users/gringocl/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/pry-0.9.12.4/lib/pry/pry_class.rb:170:in `start'
        from /Users/gringocl/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/pry-0.9.12.4/lib/pry/cli.rb:201:in `block in <top (required)>'
        from /Users/gringocl/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/pry-0.9.12.4/lib/pry/cli.rb:70:in `call'
        from /Users/gringocl/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/pry-0.9.12.4/lib/pry/cli.rb:70:in `block in parse_options'
        from /Users/gringocl/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/pry-0.9.12.4/lib/pry/cli.rb:70:in `each'
        from /Users/gringocl/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/pry-0.9.12.4/lib/pry/cli.rb:70:in `parse_options'
        from /Users/gringocl/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/pry-0.9.12.4/bin/pry:16:in `<top (required)>'
        from /Users/gringocl/.rbenv/versions/2.1.0/bin/pry:23:in `load'
        from /Users/gringocl/.rbenv/versions/2.1.0/bin/pry:23:in `<main>'

I didn't implicilty return my array in the first line. Ruby implicitly returns a value but at the end of a statement