FunctionalUtilities.h

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* (c) Copyright 1998-2019 CERN for the benefit of the LHCb and ATLAS collaborations *
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* This software is distributed under the terms of the Apache version 2 licence,     *
* copied verbatim in the file "LICENSE".                                            *
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#ifndef FUNCTIONAL_UTILITIES_H
#define FUNCTIONAL_UTILITIES_H

#include "boost/algorithm/string/join.hpp"
#include <initializer_list>
#include <string>

// TODO: fwd declare instead?
#include "GaudiAlg/GaudiAlgorithm.h"
#include "GaudiAlg/GaudiHistoAlg.h"
#include "GaudiKernel/DataObjectHandle.h"
#include "GaudiKernel/SerializeSTL.h"

namespace Gaudi::Functional {

  // This utility is needed when the inputs of a functional algorithm may be stored in several locations
  inline std::string concat_alternatives( std::initializer_list<std::string> c ) {
    return boost::algorithm::join( c, ":" );
  }

  template <typename... Strings>
  std::string concat_alternatives( const Strings&... s ) {
    return concat_alternatives( std::initializer_list<std::string>{s...} );
  }

  [[deprecated( "please use `updateHandleLocation` instead of `Gaudi::Functional::updateHandleLocation`" )]] inline void
  updateHandleLocation( IProperty& parent, const std::string& prop, const std::string& newLoc ) {
    auto sc = parent.setProperty( prop, newLoc );
    if ( sc.isFailure() ) throw GaudiException( "Could not set Property", prop + " -> " + newLoc, sc );
  }

  [[deprecated(
      "please use `updateHandleLocations` instead of `Gaudi::Functional::updateHandleLocations`" )]] inline void
  updateHandleLocations( IProperty& parent, const std::string& prop, const std::vector<std::string>& newLocs ) {
    std::ostringstream ss;
    GaudiUtils::details::ostream_joiner(
        ss << '[', newLocs, ", ", []( std::ostream & os, const auto& i ) -> auto& { return os << "'" << i << "'"; } )
        << ']';
    auto sc = parent.setProperty( prop, ss.str() );
    if ( sc.isFailure() ) throw GaudiException( "Could not set Property", prop + " -> " + ss.str(), sc );
  }

  namespace Traits {

    // traits classes used to customize Transformer and FilterPredicate
    // Define the types to to be used as baseclass, and as in- resp. output hanldes.
    // In case a type is not specified in the traits struct, a default is used.
    //
    // The defaults are:
    //
    //      using BaseClass = GaudiAlgorithm
    //      template <typename T> using InputHandle = DataObjectHandle<T>;
    //      template <typename T> using OutputHandle = DataObjectHandle<T>;
    //

    // the best way to 'compose' traits is by inheriting them one-by-one...
    template <typename... Base>
    struct use_ : Base... {};

    // helper classes one can inherit from to specify a specific trait
    template <typename Base>
    struct BaseClass_t {
      using BaseClass = Base;
    };

    template <template <typename> class Handle>
    struct InputHandle_t {
      template <typename T>
      using InputHandle = Handle<T>;
    };

    template <template <typename> class Handle>
    struct OutputHandle_t {
      template <typename T>
      using OutputHandle = Handle<T>;
    };

    // this uses the defaults -- and it itself is the default ;-)
    using useDefaults = use_<>;

    // this example uses GaudiHistoAlg as baseclass, and the default handle types for
    // input and output
    using useGaudiHistoAlg = use_<BaseClass_t<GaudiHistoAlg>>;

    // use Gaudi::Algorithm as base class -- this should be the base class!
    using useAlgorithm = use_<BaseClass_t<Gaudi::Algorithm>>;

    // use the legacy GaudiAlgorithm as base class -- this is (annoyingly) the current default
    using useLegacyGaudiAlgorithm = use_<BaseClass_t<GaudiAlgorithm>>;

  } // namespace Traits
} // namespace Gaudi::Functional

#endif