# pre_scan_tag and final_scan_tag Classes

## Summary

Types that distinguish the phases of `parallel_scan`.

## Header

     #include "tbb/parallel_scan.h"

## Syntax

    struct pre_scan_tag;
    struct final_scan_tag;

## Description

Types `pre_scan_tag` and `final_scan_tag` are dummy types used in conjunction with `parallel_scan`. See the example in the parallel_scan Template Function section for how they are used in the signature of `operator()`.

## Members

    namespace tbb {

        struct pre_scan_tag {
            static bool is_final_scan();
        };

        struct final_scan_tag {
            static bool is_final_scan();
        };

    }

The following table provides additional information on the member of this template class.
Member | Description
--- | ---
bool is_final_scan() | True for a `final_scan_tag`, otherwise false.

Parent topic: parallel_scan Template Function