AnyDataWrapper.h

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#ifndef GAUDIKERNEL_ANYDATAWRAPPER_H
#define GAUDIKERNEL_ANYDATAWRAPPER_H

// Include files
#include "GaudiKernel/DataObject.h"
#include "boost/optional.hpp"
#include <cstddef>

namespace details
{
  template <typename C>
  constexpr auto size( const C& c ) noexcept( noexcept( c.size() ) ) -> decltype( c.size() )
  {
    return c.size();
  }

  template <typename T, std::size_t N>
  constexpr auto size( const T ( &array )[N] ) noexcept
  {
    return N;
  }

  template <typename T, typename... Args>
  constexpr auto size( const T&, Args&&... ) noexcept
  {
    static_assert( sizeof...( Args ) == 0, "No extra args please" );
    return boost::none;
  }
}

// ugly hack to circumvent the usage of boost::any
struct GAUDI_API AnyDataWrapperBase : DataObject {
  // TODO:  C++17: replace with 'std::optional<std::size_t>'
  virtual boost::optional<std::size_t> size() const = 0;
};

template <class T>
class GAUDI_API AnyDataWrapper final : public AnyDataWrapperBase
{
public:
  AnyDataWrapper( T&& data ) : m_data( std::move( data ) ){};

  AnyDataWrapper( AnyDataWrapper&& other )
      : AnyDataWrapperBase( std::move( other ) ), m_data( std::move( other.m_data ) ){};

  const T& getData() const { return m_data; }
  T& getData() { return m_data; }

  boost::optional<std::size_t> size() const override
  {
    // TODO: C++17:  add 'using std::size' and remove the first two implementations in details...
    using details::size;
    return size( m_data );
  }

private:
  T m_data;
};

#endif