def variant_combinations
      combinations = []
      0.upto(2 ** FIELD_VARIANTS.length - 1) do |b|
        combinations << combination = []
        FIELD_VARIANTS.each_with_index do |variant, i|
          combination << variant if b & 1<<i > 0
        end
      end
      combinations
    end
def variant_combinations
      combinations = []
      0.upto(2 ** FIELD_VARIANTS.length - 1) do |b|
        combinations << combination = []
        FIELD_VARIANTS.each_with_index do |variant, i|
          combination << variant if b & 1<<i > 0
        end
      end
      combinations
    end
All of the possible combinations of variants