error[E0606]: cannot cast `usize` to a pointer that is wide --> $DIR/cast-macro-lhs.rs:8:23 | LL | let x = foo!() as *const [u8]; | ------ ^^^^^^^^^^^ creating a `*const [u8]` requires both an address and a length | | | consider casting this expression to `*const ()`, then using `core::ptr::from_raw_parts` error: aborting due to 1 previous error For more information about this error, try `rustc --explain E0606`.