HistogramArray.h

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/***********************************************************************************\
* (c) Copyright 1998-2022 CERN for the benefit of the LHCb and ATLAS collaborations *
*                                                                                   *
* This software is distributed under the terms of the Apache version 2 licence,     *
* copied verbatim in the file "LICENSE".                                            *
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#pragma once
 
#include <Gaudi/Accumulators/Histogram.h>
 
#include <fmt/format.h>
 
#include <utility>
 
namespace Gaudi::Accumulators {
 
  namespace details {
 
    struct FormatHistDefault {
      std::string_view text;
      FormatHistDefault( std::string_view t ) : text{ t } {}
      auto operator()( size_t n ) { return fmt::format( text, n ); }
    };
 
    template <typename Histo, std::size_t N>
    struct HistogramArrayInternal : std::array<Histo, N> {
      template <typename OWNER, typename FormatName, typename FormatTitle, std::size_t... Ns, typename... Axis,
                typename = typename std::enable_if_t<std::is_invocable_v<FormatName, int>>,
                typename = typename std::enable_if_t<std::is_invocable_v<FormatTitle, int>>>
      HistogramArrayInternal( OWNER* owner, FormatName&& fname, FormatTitle&& ftitle,
                              std::integer_sequence<std::size_t, Ns...>, Axis&&... allAxis )
          : std::array<Histo, N>{ Histo{ owner, fname( Ns ), ftitle( Ns ), allAxis... }... } {
        static_assert( sizeof...( Ns ) < 1000, "Using HistogramArray with 1000 arrays or more is prohibited. This "
                                               "would lead to very long compilation times" );
      }
      template <typename OWNER, std::size_t... Ns, typename... Axis>
      HistogramArrayInternal( OWNER* owner, std::string_view name, std::string_view title,
                              std::integer_sequence<std::size_t, Ns...>, Axis&&... allAxis )
          : std::array<Histo, N>{
                Histo{ owner, FormatHistDefault{ name }( Ns ), FormatHistDefault{ title }( Ns ), allAxis... }... } {
        static_assert( sizeof...( Ns ) < 1000, "Using HistogramArray with 1000 arrays or more is prohibited. This "
                                               "would lead to very long compilation times" );
      }
    };
  } // namespace details
 
  template <typename Histo, std::size_t N, typename Seq>
  struct HistogramArrayBase;
  template <typename Histo, std::size_t N, std::size_t... NDs>
  struct HistogramArrayBase<Histo, N, std::index_sequence<NDs...>> : details::HistogramArrayInternal<Histo, N> {
    template <typename OWNER, typename FormatName, typename FormatTitle>
    HistogramArrayBase( OWNER* owner, FormatName&& fname, FormatTitle&& ftitle,
                        details::alwaysT<NDs, typename Histo::AxisType>&&... allAxis )
        : details::HistogramArrayInternal<Histo, N>( owner, fname, ftitle, std::make_integer_sequence<std::size_t, N>{},
                                                     allAxis... ) {}
  };
  template <typename Histo, std::size_t N>
  using HistogramArray = HistogramArrayBase<Histo, N, std::make_index_sequence<Histo::NumberDimensions::value>>;
 
} // namespace Gaudi::Accumulators