flat_set.h

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// This file's extension implies that it's C, but it's really -*- C++ -*-.
/*
 * Copyright (C) 2002-2026 CERN for the benefit of the ATLAS collaboration.
 */
 
 
#ifndef CXXUTILS_FLAT_SET_H
#define CXXUTILS_FLAT_SET_H
 
#include <version>
 
#ifdef __cpp_lib_flat_set
 
// Have std::flat_set.  Put it in the CxxUtils namespace.
#include <flat_set>
namespace CxxUtils {
  using std::flat_set;
}
 
#else
 
// We don't have std::flat_set.
// Use boost::container::flat_set instead.
#include <functional>
#include <boost/container/flat_set.hpp>
namespace CxxUtils {
  // void for the third argument matches the defaults in
  // boost/container/container_fwd.hpp
  template <class KEY, class COMPARE = std::less<KEY>, class KEYCONTAINER = void>
  using flat_set = boost::container::flat_set<KEY, COMPARE, KEYCONTAINER>;
}
 
#endif
 
 
#endif // not CXXUTILS_FLAT_SET_H