controller.rb

# Instead of this...
before_all "/foo" do |env|
  puts "Setting response content type"
  env.response.content_type = "application/json"
end

# Can I do this..
before_all "/foo", &set_json # where &set_json capture the set_json method

get "/foo" do |env|
  puts env.response.content_type # => "application/json"
  {"name": "Kemal"}.to_json
end

def set_json(env)
  puts "Setting response content type"
  env.response.content_type = "application/json"
end