ClickHouse/dbms/src/AggregateFunctions/IUnaryAggregateFunction.h

#pragma once

#include <IO/WriteHelpers.h>
#include <AggregateFunctions/IAggregateFunction.h>


namespace DB
{

/** Interface for aggregate functions, that take single argument. These are almost all aggregate functions.
  */
template <typename T, typename Derived>
class IUnaryAggregateFunction : public IAggregateFunctionHelper<T>
{
private:
    Derived & getDerived() { return static_cast<Derived &>(*this); }
    const Derived & getDerived() const { return static_cast<const Derived &>(*this); }

public:
    void setArguments(const DataTypes & arguments) override final
    {
        if (arguments.size() != 1)
            throw Exception("Passed " + toString(arguments.size()) + " arguments to unary aggregate function " + this->getName(),
                ErrorCodes::NUMBER_OF_ARGUMENTS_DOESNT_MATCH);

        getDerived().setArgument(arguments[0]);
    }

    /// Accumulate a value.
    void add(AggregateDataPtr place, const IColumn ** columns, size_t row_num, Arena * arena) const override final
    {
        getDerived().addImpl(place, *columns[0], row_num, arena);
    }

    static void addFree(const IAggregateFunction * that, AggregateDataPtr place, const IColumn ** columns, size_t row_num, Arena * arena)
    {
        static_cast<const Derived &>(*that).addImpl(place, *columns[0], row_num, arena);
    }

    IAggregateFunction::AddFunc getAddressOfAddFunction() const override { return &addFree; }

    /** Implement the following in descendant class:
      * void addImpl(AggregateDataPtr place, const IColumn & column, size_t row_num, Arena * arena) const;
      * void setArgument(const DataTypePtr & argument);
      */
};

}