ESHandle.h

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#ifndef FWCore_Framework_ESHandle_h
#define FWCore_Framework_ESHandle_h
// -*- C++ -*-
//
// Package:     Framework
// Class  :     ESHandle
//
//
// Author:      Chris Jones
// Created:     Fri Apr  1 14:47:35 EST 2005
//

// system include files

// user include files
#include "FWCore/Framework/interface/ComponentDescription.h"
#include "FWCore/Framework/interface/ESHandleExceptionFactory.h"

#include <exception>
#include <memory>
#include <utility>

namespace edm {

  class ESHandleBase {
  public:
    ESHandleBase() = default;
    ESHandleBase(void const* iData, edm::eventsetup::ComponentDescription const* desc)
        : data_(iData), description_(desc) {}

    ESHandleBase(std::shared_ptr<ESHandleExceptionFactory>&& iWhyFailed) : whyFailedFactory_(std::move(iWhyFailed)) {}

    edm::eventsetup::ComponentDescription const* description() const;

    bool isValid() const { return nullptr != data_ && nullptr != description_; }

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

    explicit operator bool() const { return isValid(); }

    bool operator!() const { return not isValid(); }

    void swap(ESHandleBase& iOther) {
      std::swap(data_, iOther.data_);
      std::swap(description_, iOther.description_);
      std::swap(whyFailedFactory_, iOther.whyFailedFactory_);
    }

    std::shared_ptr<ESHandleExceptionFactory> const& whyFailedFactory() const { return whyFailedFactory_; }

  protected:
    void const* productStorage() const {
      if (whyFailedFactory_) {
        std::rethrow_exception(whyFailedFactory_->make());
      }
      return data_;
    }

  private:
    // ---------- member data --------------------------------
    void const* data_{nullptr};
    edm::eventsetup::ComponentDescription const* description_{nullptr};
    std::shared_ptr<ESHandleExceptionFactory> whyFailedFactory_{nullptr};
  };

  template <typename T>
  class ESHandle : public ESHandleBase {
  public:
    typedef T value_type;

    ESHandle() = default;
    ESHandle(T const* iData) : ESHandleBase(iData, nullptr) {}
    ESHandle(T const* iData, edm::eventsetup::ComponentDescription const* desc) : ESHandleBase(iData, desc) {}
    ESHandle(std::shared_ptr<ESHandleExceptionFactory>&&);

    // ---------- const member functions ---------------------
    T const* product() const { return static_cast<T const*>(productStorage()); }
    T const* operator->() const { return product(); }
    T const& operator*() const { return *product(); }
    // ---------- static member functions --------------------
    static constexpr bool transientAccessOnly = false;

    // ---------- member functions ---------------------------
  };

  template <class T>
  ESHandle<T>::ESHandle(std::shared_ptr<edm::ESHandleExceptionFactory>&& iWhyFailed)
      : ESHandleBase(std::move(iWhyFailed)) {}

  // Free swap function
  inline void swap(ESHandleBase& a, ESHandleBase& b) { a.swap(b); }
}  // namespace edm
#endif