BasicHandle.h

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#ifndef DataFormats_Common_BasicHandle_h
#define DataFormats_Common_BasicHandle_h

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

Handle: Shared "smart pointer" for reference to EDProducts and
their Provenances.

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

If the pointed-to EDProduct or Provenance is destroyed, use of the
Handle becomes undefined. There is no way to query the Handle to
discover if this has happened.

Handles can have:
  -- Product and Provenance pointers both null;
  -- Both pointers valid

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

If failedToGet() returns true then the requested data is not available
If failedToGet() returns false but isValid() is also false then no attempt
  to get data has occurred

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

#include "DataFormats/Provenance/interface/ProductID.h"
#include "DataFormats/Provenance/interface/Provenance.h"
#include "DataFormats/Common/interface/HandleExceptionFactory.h"
#include "FWCore/Utilities/interface/GCC11Compatibility.h"

#include <memory>

namespace cms {
  class Exception;
}

namespace edm {
  class WrapperBase;
  template <typename T>
  class Wrapper;

  class BasicHandle {
  public:
    BasicHandle() = delete;

    BasicHandle(BasicHandle const& h) = default;

    BasicHandle(BasicHandle&& h) = default;

    BasicHandle(WrapperBase const* iProd, Provenance const* iProv) noexcept(true) : product_(iProd), prov_(iProv) {}

    BasicHandle(std::shared_ptr<HandleExceptionFactory> const& iWhyFailed) noexcept(true)
        : product_(), prov_(nullptr), whyFailedFactory_(iWhyFailed) {}

    ~BasicHandle() = default;

    void swap(BasicHandle& other) noexcept(true) {
      using std::swap;
      swap(product_, other.product_);
      std::swap(prov_, other.prov_);
      swap(whyFailedFactory_, other.whyFailedFactory_);
    }

    BasicHandle& operator=(BasicHandle&& rhs) = default;
    BasicHandle& operator=(BasicHandle const& rhs) = default;

    bool isValid() const noexcept(true) { return product_ && prov_; }

    bool failedToGet() const noexcept(true) { return bool(whyFailedFactory_); }

    WrapperBase const* wrapper() const noexcept(true) { return product_; }

    Provenance const* provenance() const noexcept(true) { return prov_; }

    ProductID id() const noexcept(true) { return prov_->productID(); }

    std::shared_ptr<cms::Exception> whyFailed() const { return whyFailedFactory_->make(); }

    std::shared_ptr<HandleExceptionFactory> const& whyFailedFactory() const noexcept(true) { return whyFailedFactory_; }

    std::shared_ptr<HandleExceptionFactory>& whyFailedFactory() noexcept(true) { return whyFailedFactory_; }

    void clear() noexcept(true) {
      product_ = nullptr;
      prov_ = nullptr;
      whyFailedFactory_.reset();
    }

    static BasicHandle makeInvalid() { return BasicHandle(true); }

  private:
    //This is used to create a special invalid BasicHandle
    explicit BasicHandle(bool) : product_(nullptr) {}
    WrapperBase const* product_;
    Provenance const* prov_;
    std::shared_ptr<HandleExceptionFactory> whyFailedFactory_;
  };

  // Free swap function
  inline void swap(BasicHandle& a, BasicHandle& b) noexcept(true) { a.swap(b); }
}  // namespace edm

#endif