error[E0054]: cannot cast `i32` as `bool`
  --> $DIR/cast-rfc0401-2.rs:6:13
   |
LL |     let _ = 3 as bool;
   |             ^^^^^^^^^
   |
help: compare with zero instead
   |
LL |     let _ = 3 != 0;
   |               ~~~~

error: aborting due to previous error

For more information about this error, try `rustc --explain E0054`.