GenCrossSections ambiguous

Hi,

so if I understood the code correctly, the GenCrossSection::set_cross_section() method will just pretend that every weight has the same cross-section since it sets them all to the same value.

Then, there is a method for the generators to overwrite these cross-sections again on a member-by-member basis, but there's no guarantee that they will actually do this. In fact, this wasn't even an option in the past, so if I read a HepMC2 file - which only has a single cross-section - with HepMC3, I will apparently always get a vector with the same cross-section value for each weight, when I would have expected the vector to have size 1, no?

How can one programatically distinguish the case of "there was only one cross-section provided by the generator" vs "the generator provided the different cross-sections for each weight"?

Cheers, Chris