The resulting argument pack is passed as the constructor parameter to all the accumulators in the set. Your accumulator can then extract the coefficients argument from the pack with "args[coefficients]".
Done this, but I want to pass an array of values to coefficients, ie it looks like, eg: array<double,5> coeffs={0.1,0.2,0.1}; accumulator_set<... > acc( .., coefficients = coeffs, ...); So far so good. My filter depends on the delay buffer I have defined which has the cache_size constructor argument. Since I am specifying the list of coefficients, I want the cache_size to be set to the number of elements in my coefficient list, with out having to specify it, ie without having to write: array<double,5> coeffs={0.1,0.2,0.1}; accumulator_set<... > acc( .., coefficients = coeffs, cache_size=5...); Not sure if this is possible through boost::Parameters (first time I have seen this used, BTW, I'm impressed), or if I need to have the filter access the delay post construction, or if it is just not possible.