error[E0435]: attempt to use a non-constant value in a constant --> $DIR/E0435.rs:5:17 | LL | let foo: usize = 42; | ------- help: consider using `const` instead of `let`: `const foo` LL | let _: [u8; foo]; | ^^^ non-constant value error: aborting due to 1 previous error For more information about this error, try `rustc --explain E0435`.