error: generic parameters may not be used in const operations --> $DIR/issue-68366.rs:11:37 | LL | impl Collatz<{Some(N)}> {} | ^ cannot perform const operation using `N` | = help: const parameters may only be used as standalone arguments, i.e. `N` = help: use `#![feature(generic_const_exprs)]` to allow generic const expressions error[E0207]: the const parameter `N` is not constrained by the impl trait, self type, or predicates --> $DIR/issue-68366.rs:11:7 | LL | impl Collatz<{Some(N)}> {} | ^^^^^^^^^^^^^^ unconstrained const parameter | = note: expressions using a const parameter must map each value to a distinct output value = note: proving the result of expressions other than the parameter are unique is not supported error[E0207]: the const parameter `N` is not constrained by the impl trait, self type, or predicates --> $DIR/issue-68366.rs:17:6 | LL | impl Foo {} | ^^^^^^^^^^^^^^ unconstrained const parameter | = note: expressions using a const parameter must map each value to a distinct output value = note: proving the result of expressions other than the parameter are unique is not supported error: aborting due to 3 previous errors For more information about this error, try `rustc --explain E0207`.