Generic Const Args and You
Rust’s const-generics group has prototyped a family of features for using generic-dependent values in const-generic positions, where stable Rust currently permits only bare parameters or fully concrete constants. The proposal covers constructing arrays, tuples, and ADTs in const arguments, and using const items and associated constants; it is intended to replace the long-running generic_const_exprs experiment.
The design is still very unstable: most examples require an explicit gca!(...) marker, arithmetic and function calls are not directly supported there, and the project says none of the features is ready for stabilization or even an RFC. A smaller gca_min_const_items variant trades expressiveness for simpler equality rules and a path toward earlier stabilization.
Lobsters commenters welcomed the added expressiveness, but asked why the explicit macro is necessary and what type-system constraint prevents cleaner syntax. Another commenter noted that practical arithmetic-dependent array lengths still require the full const-items feature, and asked for a clearer use case for the minimal variant.