Make GenericParameters return optional instead of empty defaults on non-existant keys

[tmadlener]

BEGINRELEASENOTES

• Make the GenericParameters return std::optional on non-existant keys instead of empty defaults. This allows to differentiate between empty (but set) and unset parameters, as the default value could actually be a valid parameter value for some types (e.g. integers or floats).
  • Rename the setValue and getValue functions to just set and get. This is also a breaking change, but as far as we are aware the GenericParameters are only used internally in podio.
• Make the Frame::getParameter also return this std::optional. This is a breaking change that might require adaptation of existing code

ENDRELEASENOTES

Fixes #576

The following PRs make this introduction work transparently and need to be merged first to not break the nightlies

• [x] https://github.com/key4hep/EDM4hep/pull/305
• [x] https://github.com/AIDASoft/DD4hep/pull/1264
• [x] https://github.com/key4hep/k4FWCore/pull/195
• [x] https://github.com/key4hep/k4Clue/pull/59
• [x] https://github.com/key4hep/k4EDM4hep2LcioConv/pull/64

[m-fila]

I think getValue is an unintuitive name for a method returning optional instead of "value". Code like parameter.GetValue<int>("foo").has_value() reads a bit awkward

[tmadlener]

Since we are breaking interfaces in any case I don't mind different names. That would in principle allow us to properly deprecate getValue as it is. On the other hand GenericParameters is mainly used internally, so we could probably also just use new names without deprecation.

[hegner]

@tmadlener - ping. What's the status?

[tmadlener]

Currently testing what is breaking downstream (and then fixing that if necessary)

[tmadlener]

I think getValue is an unintuitive name for a method returning optional instead of "value". Code like parameter.GetValue<int>("foo").has_value() reads a bit awkward

I have changed this to get as we are breaking things in any case

[tmadlener]

@Zehvogel a quick heads up:

• Rename the setValue and getValue functions to just set and get. This is also a breaking change, but as far as we are aware the GenericParameters are only used internally in podio.

This bit here will require some changes to your RDataFrame code where you directly talk to the PARAMETERS branch, mainly

- df = df.Define("xsec_fb", "PARAMETERS.getValue<float>(\"crossSection\")")
+ df = df.Define("xsec_fb", "PARAMETERS.get<float>(\"crossSection\")")

[Zehvogel]

This bit here will require some changes to your RDataFrame code where you directly talk to the PARAMETERS branch, mainly

actually needed a

- df = df.Define("xsec_fb", "PARAMETERS.getValue<float>(\"crossSection\")")
+ df = df.Define("xsec_fb", "*PARAMETERS.get<float>(\"crossSection\")")

(or something intelligent :))

[tmadlener]

Ah yes, because it now also returns a std::optional. so, either operator* (as in your diff) or .value() will get you the actual value and not the optional).