ESWatcher.h

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#ifndef Framework_ESWatcher_h
#define Framework_ESWatcher_h
// -*- C++ -*-
//
// Package:     Framework
// Class  :     ESWatcher
//
//
// Original Author:  Chris Jones
//         Created:  Fri Sep 22 18:19:24 EDT 2006
//

// system include files
#include <functional>

// user include files
#include "FWCore/Framework/interface/EventSetup.h"

// forward declarations

namespace edm {
  template <class T>
  class ESWatcher {
  public:
    struct NullFunction {
      void operator()(const T&) {}
    };

    ESWatcher() : callback_(NullFunction()), cacheId_(0) {}

    template <class TFunc>
    ESWatcher(TFunc iFunctor) : callback_(iFunctor), cacheId_(0) {}

    template <class TObj, class TMemFunc>
    ESWatcher(TObj const& iObj, TMemFunc iFunc)
        : callback_(std::bind(iFunc, iObj, std::placeholders::_1)), cacheId_(0) {}
    //virtual ~ESWatcher();

    // ---------- const member functions ---------------------

    // ---------- static member functions --------------------

    // ---------- member functions ---------------------------
    bool check(const edm::EventSetup& iSetup) {
      const T& record = iSetup.template get<T>();
      bool result = cacheId_ != record.cacheIdentifier();
      if (result) {
        callback_(record);
      }
      cacheId_ = record.cacheIdentifier();
      return result;
    }

  private:
    ESWatcher(const ESWatcher&) = delete;  // stop default

    const ESWatcher& operator=(const ESWatcher&) = delete;  // stop default

    // ---------- member data --------------------------------
    std::function<void(const T&)> callback_;
    unsigned long long cacheId_;
  };
}  // namespace edm

#endif