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## Struct template accumulator_set

boost::accumulators::accumulator_set — A set of accumulators.

## Synopsis

    // In header: <boost/accumulators/framework/accumulator_set.hpp>

    template<typename Sample, typename Features, typename Weight>
    struct accumulator_set {
      // types
      typedef Sample   sample_type;    // The type of the samples that will be accumulated.
      typedef Features features_type;  // An MPL sequence of the features that should be accumulated.
      typedef Weight   weight_type;    // The type of the weight parameter. Must be a scalar. Defaults to void.
      typedef void result_type;

      // member classes/structs/unions
      template<typename Feature>
      struct apply {
      };

      // construct/copy/destruct
      template<typename A1> explicit accumulator_set(A1 const &);

      // public member functions
      template<typename UnaryFunction> void visit(UnaryFunction const &);
      template<typename FilterPred, typename UnaryFunction>
        void visit_if(UnaryFunction const &);
      void operator()();
      template<typename A1> void operator()(A1 const &);
      template<typename Feature> apply< Feature >::type & extract();
      template<typename Feature> apply< Feature >::type const & extract() const;
      template<typename Feature> void drop();
    };

## Description

accumulator_set resolves the dependencies between features and ensures that the accumulators in the set are updated in the proper order.

acccumulator_set provides a general mechanism to visit the accumulators in the set in order, with or without a filter. You can also fetch a reference to an accumulator that corresponds to a feature.

### `accumulator_set` public types

1. typedef void result_type;

   The return type of the operator() overloads is void.

### `accumulator_set` public construct/copy/destruct

1.     template<typename A1> explicit accumulator_set(A1 const & a1);

   This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

   Parameters:

   `a1` | Optional named parameter to be passed to all the accumulators

### `accumulator_set` public member functions

1.     template<typename UnaryFunction> void visit(UnaryFunction const & func);

   Visitation

   Parameters:

   `func` | UnaryFunction which is invoked with each accumulator in turn.

2.     template<typename FilterPred, typename UnaryFunction>
         void visit_if(UnaryFunction const & func);

   Conditional visitation

   Parameters:

   `func` | UnaryFunction which is invoked with each accumulator in turn, provided the accumulator satisfies the MPL predicate FilterPred.

3.     void operator()();

   Accumulation

4.     template<typename A1> void operator()(A1 const & a1);

5.     template<typename Feature> apply< Feature >::type & extract();

   Extraction

6.     template<typename Feature> apply< Feature >::type const & extract() const;

   This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

7.     template<typename Feature> void drop();

   Drop