Now I am trying to describe Boost.accumulators. roc_distribution To define ROC curve data, we need two p_square_cumulative_distribution 1. cumulative_distribution ture or false potive 2. cumulative_distribution ture or false negative One of the cumulative_distribution can be defined by using dependencies struct roc_distribution : depends_on< p_square_cumulative_distribution > … But I can not find way to use two different cumulative_distribution in single acc class. How to use two different cumulative_distribution in single acc class like the following ? struct roc_distribution_impl... { template<typename Args> void operator ()(Args const &args,bool positive_or_negative) if(positive_or_negative) positive_p_square_cumulative_distribution … else negative_p_square_cumulative_distribution … … }