Consider making zero-field data classes not allocate anything

[densh]

This has been previously explored in rust. Effectively zero-size data classes would become first-class equivalent of Unit. Allocation would not call allocate on allocator as followers of zero-size types are never followed. Fields of zero-size types are also zero-size making it very useful feature to augment specialisation.

Unfortunately this has some non-trivial feature interactions wrt current layout machinery that might need a complete rewrite to support this. Right now there is no compelling use case to do this but the idea is quite interesting and might be explored in the future.

[DarkDimius]

I'd say that as zero-size data classes are observationally equivalent, they can simply be replaced by singleton objects. Which could be either stored on-heap or off-heap.