Provide a way in configuration validation to specify containers of a set length

[Dr15Jones]

There are times where a container of parameters is required to be of a set length. We'd like to have the configuration validation system be able to enforce such a requirement. One suggestion was to possibly allow the use of std::array<> as a C++ parameter type.

[cmsbuild]

A new Issue was created by @Dr15Jones (Chris Jones).

@davidlange6, @smuzaffar, @Degano, @davidlt, @Dr15Jones can you please review it and eventually sign/assign? Thanks.

cms-bot commands are listed here

[Dr15Jones]

assign core

[cmsbuild]

New categories assigned: core

@Dr15Jones,@smuzaffar you have been requested to review this Pull request/Issue and eventually sign? Thanks

[Dr15Jones]

The problem with using std::array<> as a drop in replacement for std::vector<> is the type specified in the python configuration is a one to one mapping to a C++ type. If we were to allow one python type to be used by multiple C++ types the system couldn't properly enforce that the same C++ type was used every single time that parameter is requested.

This does bring up the possibility that we abandon the need for standard types to be specified in the python. When converting from the python values to C++ we just enforce that the types are convertible (e.g. python int into a C++ float). The parameter system of the other framework at FNAL (derived originally from CMSSW) usage such a system.

[smuzaffar]

@Dr15Jones , @makortel was this implemented?

[makortel]

In the configuration validation system no, but in the configuration reading phase yes, first in #22362 and then improved in #31429.

[fwyzard]

Thanks Matti, I had missed the second part... I've made #35316 to use the new functionality.