values.h

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#ifndef LARCOREALG_COREUTILS_VALUES_H
#define LARCOREALG_COREUTILS_VALUES_H

// LArSoft libraries
#include "larcorealg/CoreUtils/get_elements.h"
#include "larcorealg/CoreUtils/span.h" // util::make_transformed_span()

// C/C++ libraries
#include <cstddef> // std::size_t
#include <map>
#include <tuple> // std::get()
#include <type_traits>
#include <unordered_map>
#include <utility> // std::forward(), std::as_const()

namespace util {

  // -- BEGIN -- Transformed iterations ----------------------------------------

  template <typename Coll>
  decltype(auto) values(Coll&& coll);

  template <typename Coll>
  decltype(auto) const_values(Coll&& coll);

  // -- END -- Transformed iterations ------------------------------------------

} // namespace util

//==============================================================================
//=== template implementation
//==============================================================================
//------------------------------------------------------------------------------
//--- util::values()
//------------------------------------------------------------------------------
namespace util::details {

  //----------------------------------------------------------------------------
  template <typename Coll, typename = void>
  struct values_impl {

    template <typename T>
    static constexpr decltype(auto) iterate(T&& coll) noexcept
    {
      return coll;
    }

  }; // struct values_impl

  //----------------------------------------------------------------------------
  template <typename Map, std::size_t NElement = 1U>
  struct map_values_impl {

    template <typename T>
    static constexpr decltype(auto) iterate(T&& coll) noexcept
    {
      return util::get_elements<NElement>(std::forward<T>(coll));
    }

  }; // map_values_impl

  //----------------------------------------------------------------------------
  template <typename Key, typename Value, typename... Args>
  struct values_impl<std::map<Key, Value, Args...>>
    : map_values_impl<std::map<Key, Value, Args...>> {};
  template <typename Key, typename Value, typename... Args>
  struct values_impl<std::unordered_map<Key, Value, Args...>>
    : map_values_impl<std::unordered_map<Key, Value, Args...>> {};

  //----------------------------------------------------------------------------

} // namespace util::details

//------------------------------------------------------------------------------
template <typename Coll>
decltype(auto) util::values(Coll&& coll)
{
  return details::values_impl<std::decay_t<Coll>>::iterate(std::forward<Coll>(coll));
} // util::values()

//------------------------------------------------------------------------------
template <typename Coll>
decltype(auto) util::const_values(Coll&& coll)
{
  return values(std::as_const(coll));
}

//------------------------------------------------------------------------------

#endif // LARCOREALG_COREUTILS_VALUES_H