Rails multiple request variants

application_controler.rb

# This code is an example to combine different variants from different reasons into the request.variant setting from Rails 4.1

before_action :set_versions

def set_versions
  # First, we load all the variants from whatever our variant logic is (mobile support, tests ab, beta versions...)
  variants = []
  variants << params[:b].to_sym if params[:b]
  variants << params[:a].to_sym if params[:a]

  # Now, we combine the variants
  combined_variants = []

  variants.length.times do |i|
    combined_variants << variants.combination(i+1).to_a
  end

  combined_variants = combined_variants.reverse.flatten(1)
  combined_variants = combined_variants.map{|v| v.join("+").to_sym}
  
  # and assign the request.variant
  request.variant = combined_variants
end