Traits are defined in such a way that they can be flattened.

At the moment this does not happen at load time as you assume, but at 
the time at which the mcz creation. This means that pre-traits MC works 
unchanged with flat mcz files, at the cost of needing to create flat and 
unflat variations on each.

Daniel

Andreas Raab wrote:
> Adrian Lienhard wrote:
>> If the package does not include any traits it should work also in 
>> previous images. If this is not the case let me know. Of course if 
>> you have traits, you cannot just load that into a pre 3.9 image.
>
> Why not? Wasn't the idea that traits methods get "inlined" when they 
> are loaded into older versions? And if it's about the traits 
> definition itself, a little compatibility package (introducing class 
> Trait and just treat the traits defined in the package as subclasses) 
> should go a long way.
>
> Cheers,
>   - Andreas
>