error[E0308]: mismatched types
  --> $DIR/static-reference-to-fn-1.rs:17:15
   |
LL |         func: &foo,
   |               ^^^^ expected `&fn() -> Option<isize>`, found `&fn() -> Option<isize> {foo}`
   |
   = note: expected reference `&fn() -> Option<isize>`
              found reference `&fn() -> Option<isize> {foo}`
   = note: fn items are distinct from fn pointers
   = note: when the arguments and return types match, functions can be coerced to function pointers
help: consider casting to a fn pointer
   |
LL |         func: &(foo as fn() -> Option<isize>),
   |               ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

error: aborting due to previous error

For more information about this error, try `rustc --explain E0308`.