Common/interface/HandleBase.h

0001 #ifndef DataFormats_Common_interface_HandleBase_h
0002 #define DataFormats_Common_interface_HandleBase_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 <algorithm>
0029 #include <cassert>
0030 #include <memory>
0031
0032 #include "DataFormats/Provenance/interface/ProductID.h"
0033 #include "DataFormats/Provenance/interface/ProvenanceFwd.h"
0034 #include "DataFormats/Common/interface/HandleExceptionFactory.h"
0035
0036 namespace cms {
0037   class Exception;
0038 }
0039
0040 namespace edm {
0041   class HandleBase {
0042   public:
0043     HandleBase() : product_(nullptr), prov_(nullptr) {}
0044
0045     HandleBase(void const* prod, Provenance const* prov) : product_(prod), prov_(prov) {
0046       assert(prod);
0047       assert(prov);
0048     }
0049
0050     ///Used when the attempt to get the data failed
0051     HandleBase(std::shared_ptr<HandleExceptionFactory const>&& iWhyFailed)
0052         : product_(nullptr), prov_(nullptr), whyFailedFactory_(iWhyFailed) {}
0053
0054     void clear() {
0055       product_ = nullptr;
0056       prov_ = nullptr;
0057       whyFailedFactory_.reset();
0058     }
0059
0060     void swap(HandleBase& other) {
0061       std::swap(product_, other.product_);
0062       std::swap(prov_, other.prov_);
0063       std::swap(whyFailedFactory_, other.whyFailedFactory_);
0064     }
0065
0066     bool isValid() const { return product_ && prov_; }
0067
0068     bool failedToGet() const { return bool(whyFailedFactory_); }
0069
0070     Provenance const* provenance() const { return prov_; }
0071
0072     ProductID id() const;
0073
0074     std::shared_ptr<cms::Exception> whyFailed() const {
0075       if (whyFailedFactory_.get()) {
0076         return whyFailedFactory_->make();
0077       }
0078       return std::shared_ptr<cms::Exception>();
0079     }
0080
0081     std::shared_ptr<HandleExceptionFactory const> const& whyFailedFactory() const { return whyFailedFactory_; }
0082
0083     explicit operator bool() const { return isValid(); }
0084
0085     bool operator!() const { return not isValid(); }
0086
0087   protected:
0088     void const* productStorage() const;
0089
0090   private:
0091     void const* product_;
0092     Provenance const* prov_;
0093     std::shared_ptr<HandleExceptionFactory const> whyFailedFactory_;
0094   };
0095
0096   // Free swap function
0097   inline void swap(HandleBase& a, HandleBase& b) { a.swap(b); }
0098
0099 }  // namespace edm
0100
0101 #endif  // DataFormats_Common_interface_HandleBase_h