Framework/interface/data_default_record_trait.h

0001 #ifndef Framework_data_default_record_trait_h
0002 #define Framework_data_default_record_trait_h
0003 // -*- C++ -*-
0004 //
0005 // Package:     Framework
0006 // Class  :     data_default_record_trait
0007 //
0008 /**\class data_default_record_trait data_default_record_trait.h FWCore/Framework/interface/data_default_record_trait.h
0009
0010  Description: trait class that assigns a default EventSetup Record to a particular data type
0011
0012  Usage:
0013     Many types of data in a EventSetup are only available in one Record type.  For example, the HCal Alignment
0014   data only appears in the HCal Alignment Record. For such cases, it is annoying for users to have to specify
0015   both the Record and the Data type in order to get the data.  In such a case, a specialization of
0016   data_default_record_trait for that data type can be assigned to allow access 'direct' access to that data
0017   from the EventSetup
0018
0019   ESHandle<MyData> pMyData;
0020   eventSetup.getData(pMyData);
0021
0022   which is just a short hand for
0023
0024   ESHandle<MyData> pMyData;
0025   eventSetup.get<MyDataRecord>.get(pMyData);
0026
0027     To specify the default record, you must use the macro EVENTSETUP_DATA_DEFAULT_RECORD in the header file for
0028   the data (or in a header file that users will include).  For Example
0029
0030
0031     #include "..../MyDataRecord.h"
0032
0033     class MyData { ...
0034     };
0035
0036     EVENTSETUP_DATA_DEFAULT_RECORD(MyData, MyDataRecord);
0037 */
0038 //
0039 // Author:      Chris Jones
0040 // Created:     Thu Apr  7 07:59:56 CDT 2005
0041 //
0042
0043 namespace edm {
0044
0045   template <typename T>
0046   class ESHandle;
0047
0048   // Special class to denote that the default record should be used.
0049   struct DefaultRecord {};
0050
0051   namespace eventsetup {
0052     template <class T>
0053     struct MUST_GET_RECORD_FROM_EVENTSETUP_TO_GET_DATA;
0054
0055     template <class DataT>
0056     struct data_default_record_trait {
0057       //NOTE: by default, a data item does not have a default record
0058       typedef MUST_GET_RECORD_FROM_EVENTSETUP_TO_GET_DATA<DataT> type;
0059     };
0060
0061     template <typename T>
0062     struct default_record {
0063       using data_type = typename T::value_type;
0064       using RecordT = typename eventsetup::data_default_record_trait<data_type>::type;
0065     };
0066
0067     template <typename T>
0068     using default_record_t = typename default_record<T>::RecordT;
0069   }  // namespace eventsetup
0070
0071   template <typename T>
0072   struct ESHandleAdapter {
0073     using value_type = T;
0074   };
0075 }  // namespace edm
0076
0077 #define EVENTSETUP_DATA_DEFAULT_RECORD(_data_, _record_) \
0078   namespace edm::eventsetup {                            \
0079     template <>                                          \
0080     struct data_default_record_trait<_data_> {           \
0081       typedef _record_ type;                             \
0082     };                                                   \
0083   }
0084
0085 #endif