error[E0015]: cannot call non-const closure in constants --> $DIR/issue-93647.rs:2:5 | LL | (||1usize)() | ^^^^^^^^^^^^ | = note: closures need an RFC before allowed to be called in constants = note: calls in constants are limited to constant functions, tuple structs and tuple variants = help: add `#![feature(const_trait_impl)]` to the crate attributes to enable error: aborting due to 1 previous error For more information about this error, try `rustc --explain E0015`.