error[E0277]: expected a `FnOnce()` closure, found `{integer}`
  --> $DIR/closure-expected.rs:3:23
   |
LL |     let y = x.or_else(4);
   |               ------- ^ expected an `FnOnce()` closure, found `{integer}`
   |               |
   |               required by a bound introduced by this call
   |
   = help: the trait `FnOnce()` is not implemented for `{integer}`
   = note: wrap the `{integer}` in a closure with no arguments: `|| { /* code */ }`
note: required by a bound in `Option::<T>::or_else`
  --> $SRC_DIR/core/src/option.rs:LL:COL

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0277`.