The following program surprisingly does not compile: ```rust fn main() { let x = &mut 2; let _val = {{x} as *mut i32}; } ``` The error is rather confusing, somehow it expects something to be `()`: ``` error: expected expression, found keyword `as` --> src/main.rs:3:21 | 3 | let _val = {{x} as *mut i32}; | ^^ expected expression error[E0308]: mismatched types --> src/main.rs:3:18 | 1 | fn main() { | - expected `()` because of default return type 2 | let x = &mut 2; 3 | let _val = {{x} as *mut i32}; | ^ expected (), found mutable reference | = note: expected type `()` found type `&mut {integer}` ``` If I remove either of the pair of braces in the last line, it works as expected.