FunctionalUtilities.h

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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
{
  namespace 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...} );
    }

    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 );
    }

    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 );
    }

    [[deprecated( "please use updateHandleLocation instead" )]] inline void
    updateReadHandleLocation( IProperty& parent, const std::string& prop, const std::string& newLoc )
    {
      return updateHandleLocation( parent, prop, newLoc );
    }

    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>>;
    }
  }
}

#endif