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Update HepMC::uniqueID helper function to cope with xAOD::TruthParticle and xAOD::TruthVertex

John Derek Chapman requested to merge jchapman/athena:uniqueID_enable_if_t_main into main

Background:

  • HepMC2 GenVertex has a barcode() method (returns a manually set unique identifier) and an id() method which was used to hold the "status" of the GenVertex (basically indicated the process which caused the decay/interaction represented by the vertex).\
  • HepMC3 GenVertex has an id() method (returns an automatically set unique identifier) and a status() method which is used to hold the "status" of the GenVertex().\
  • xAOD::TruthVertex is based on HepMC2 GenVertex, so has corresponding barcode() and id() methods.

This merge request updates the HepMC::uniqueID(const T& p) function to handle xAOD::TruthParticle and xAOD::TruthVertex in a robust way (returning barcode() rather than id()). NB some care is required when comparing unique identifiers for HepMC::GenParticle/Vertex with their xAOD::Truth equivalents.

Also add HepMC::status(const T& p) to simplify acessing "status" for xAOD::TruthVertex and HepMC2 GenVertex.

Follows the clean-up in !72007 (merged) and needed to simplify !67195 where we are attempting to migrate xAOD::TruthVertex to be more like HepMC3::GenVertex.

Edited by John Derek Chapman

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