[hatmatrix]

True, actually they are good in following up on numerical correctness, so I should be rephrase 'correctness in computation' to 'correctness in composition' - the types of bugs that arise from mashing a lot of modules together. On the one hand it's not a Julia issue but a package ecosystem issue.

I think you're actually even more active in the Julia community so maybe I don't have to summarize the debate but these are the types of traits and interface packages being developed that are meant to formalize how modules can be used and extended by others.

https://github.com/rafaqz/Interfaces.jl

https://discourse.julialang.org/t/interfaces-traits-in-julia...

[nsajko]

What I wanted to say is that I'm skeptical regarding "interfaces", either as a language feature or as a package. Although TBH I have not yet given any specific "interfaces" design more than a cursory glance, so my position is not really justified.