mapper.rb

        def matches?(env)
          req = @request.new(env)

          @constraints.each { |constraint|
            if constraint.respond_to?(:matches?) && !constraint.matches?(req)
              return false
            elsif constraint.respond_to?(:call) && !constraint.call(*constraint_args(constraint, req))
              return false
            end
          }

          return true
        ensure
          req.reset_parameters
        end