Common/interface/Handle.h

0001 #ifndef DataFormats_Common_Handle_h
0002 #define DataFormats_Common_Handle_h
0003
0004 /*----------------------------------------------------------------------
0005
0006 Handle: Non-owning "smart pointer" for reference to Products and
0007 their Provenances.
0008
0009 This is a very preliminary version, and lacks safety features and
0010 elegance.
0011
0012 If the pointed-to Product or Provenance is destroyed, use of the
0013 Handle becomes undefined. There is no way to query the Handle to
0014 discover if this has happened.
0015
0016 Handles can have:
0017   -- Product and Provenance pointers both null;
0018   -- Both pointers valid
0019
0020 To check validity, one can use the isValid() function.
0021
0022 If failedToGet() returns true then the requested data is not available
0023 If failedToGet() returns false but isValid() is also false then no attempt
0024   to get data has occurred
0025
0026 ----------------------------------------------------------------------*/
0027
0028 #include "DataFormats/Common/interface/HandleBase.h"
0029
0030 namespace edm {
0031
0032   template <typename T>
0033   class Handle : public HandleBase {
0034   public:
0035     using element_type = T;
0036
0037     // Default constructed handles are invalid.
0038     Handle();
0039
0040     Handle(T const* prod, Provenance const* prov);
0041
0042     Handle(std::shared_ptr<HandleExceptionFactory const>&&);
0043     Handle(Handle const&) = default;
0044     Handle& operator=(Handle&&) = default;
0045     Handle& operator=(Handle const&) = default;
0046
0047     ~Handle();
0048
0049     T const* product() const;
0050     T const* operator->() const;  // alias for product()
0051     T const& operator*() const;
0052
0053   private:
0054   };
0055
0056   template <class T>
0057   Handle<T>::Handle() : HandleBase() {}
0058
0059   template <class T>
0060   Handle<T>::Handle(T const* prod, Provenance const* prov) : HandleBase(prod, prov) {}
0061
0062   template <class T>
0063   Handle<T>::Handle(std::shared_ptr<edm::HandleExceptionFactory const>&& iWhyFailed)
0064       : HandleBase(std::move(iWhyFailed)) {}
0065
0066   template <class T>
0067   Handle<T>::~Handle() {}
0068
0069   template <class T>
0070   T const* Handle<T>::product() const {
0071     return static_cast<T const*>(productStorage());
0072   }
0073
0074   template <class T>
0075   T const* Handle<T>::operator->() const {
0076     return product();
0077   }
0078
0079   template <class T>
0080   T const& Handle<T>::operator*() const {
0081     return *product();
0082   }
0083 }  // namespace edm
0084 #endif