D has had support for pre/post contracts and invariants for a long time, but I haven't seen them used in many projects. I think it's one of those niche uses, or

D has had support for pre/post contracts and invariants for a long time, but I haven't seen them used in many projects. I think it's one of those niche uses, or something that sounds like it'd be fun to have but in the end ends up being annoying to maintain.