OrphanHandleBase.h

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#ifndef DataFormats_Common_OrphanHandleBase_h
#define DataFormats_Common_OrphanHandleBase_h

/*----------------------------------------------------------------------
  
OrphanHandle: Non-owning "smart pointer" for reference to EDProducts.

This is a very preliminary version, and lacks safety features and
elegance.

If the pointed-to WrapperBase is destroyed, use of the OrphanHandle
becomes undefined. There is no way to query the OrphanHandle to
discover if this has happened.

OrphanHandles can have:
  -- Product pointer null and id == 0;
  -- Product pointer valid and id != 0;

To check validity, one can use the isValid() function.

----------------------------------------------------------------------*/

#include "DataFormats/Provenance/interface/ProductID.h"
#include <cassert>
#include <algorithm>

namespace edm {
  class OrphanHandleBase {
  public:
    OrphanHandleBase() :
      product_(), id_(ProductID()) {
    }

    OrphanHandleBase(void const* iProd, ProductID const& iId) :
      product_(iProd), id_(iId) {
      assert(iProd);
    }

    ~OrphanHandleBase() {}

    void clear() {
      product_ = nullptr;
      id_ = ProductID();
    }

    void swap(OrphanHandleBase& other) {
      using std::swap;
      swap(product_, other.product_);
      std::swap(id_, other.id_);
    }
    
    OrphanHandleBase& operator=(OrphanHandleBase const& rhs) {
      OrphanHandleBase temp(rhs);
      this->swap(temp);
      return *this;
    }

    bool isValid() const {
      return product_ && id_ != ProductID();
    }

    ProductID id() const;

  protected:
    void const* productStorage() const;

  private:
    void const* product_;
    ProductID id_;
  };

  // Free swap function
  inline
  void
  swap(OrphanHandleBase& a, OrphanHandleBase& b) {
    a.swap(b);
  }
}

#endif