error[E0277]: expected a `std::ops::Fn<(&isize,)>` closure, found `for<'r> unsafe fn(&'r isize) -> isize {square}`
  --> $DIR/unboxed-closures-unsafe-extern-fn.rs:12:21
   |
LL | fn call_it<F:Fn(&isize)->isize>(_: &F, _: isize) -> isize { 0 }
   |    -------   ----------------- required by this bound in `call_it`
...
LL |     let x = call_it(&square, 22);
   |                     ^^^^^^^ expected an `Fn<(&isize,)>` closure, found `for<'r> unsafe fn(&'r isize) -> isize {square}`
   |
   = help: the trait `for<'r> std::ops::Fn<(&'r isize,)>` is not implemented for `for<'r> unsafe fn(&'r isize) -> isize {square}`

error[E0277]: expected a `std::ops::FnOnce<(&isize,)>` closure, found `for<'r> unsafe fn(&'r isize) -> isize {square}`
  --> $DIR/unboxed-closures-unsafe-extern-fn.rs:12:21
   |
LL | fn call_it<F:Fn(&isize)->isize>(_: &F, _: isize) -> isize { 0 }
   |    -------               ----- required by this bound in `call_it`
...
LL |     let x = call_it(&square, 22);
   |                     ^^^^^^^ expected an `FnOnce<(&isize,)>` closure, found `for<'r> unsafe fn(&'r isize) -> isize {square}`
   |
   = help: the trait `std::ops::FnOnce<(&isize,)>` is not implemented for `for<'r> unsafe fn(&'r isize) -> isize {square}`

error[E0277]: expected a `std::ops::FnMut<(&isize,)>` closure, found `for<'r> unsafe fn(&'r isize) -> isize {square}`
  --> $DIR/unboxed-closures-unsafe-extern-fn.rs:18:25
   |
LL | fn call_it_mut<F:FnMut(&isize)->isize>(_: &mut F, _: isize) -> isize { 0 }
   |    -----------   -------------------- required by this bound in `call_it_mut`
...
LL |     let y = call_it_mut(&mut square, 22);
   |                         ^^^^^^^^^^^ expected an `FnMut<(&isize,)>` closure, found `for<'r> unsafe fn(&'r isize) -> isize {square}`
   |
   = help: the trait `for<'r> std::ops::FnMut<(&'r isize,)>` is not implemented for `for<'r> unsafe fn(&'r isize) -> isize {square}`

error[E0277]: expected a `std::ops::FnOnce<(&isize,)>` closure, found `for<'r> unsafe fn(&'r isize) -> isize {square}`
  --> $DIR/unboxed-closures-unsafe-extern-fn.rs:18:25
   |
LL | fn call_it_mut<F:FnMut(&isize)->isize>(_: &mut F, _: isize) -> isize { 0 }
   |    -----------                  ----- required by this bound in `call_it_mut`
...
LL |     let y = call_it_mut(&mut square, 22);
   |                         ^^^^^^^^^^^ expected an `FnOnce<(&isize,)>` closure, found `for<'r> unsafe fn(&'r isize) -> isize {square}`
   |
   = help: the trait `std::ops::FnOnce<(&isize,)>` is not implemented for `for<'r> unsafe fn(&'r isize) -> isize {square}`

error[E0277]: expected a `std::ops::FnOnce<(&isize,)>` closure, found `for<'r> unsafe fn(&'r isize) -> isize {square}`
  --> $DIR/unboxed-closures-unsafe-extern-fn.rs:24:26
   |
LL | fn call_it_once<F:FnOnce(&isize)->isize>(_: F, _: isize) -> isize { 0 }
   |    ------------                   ----- required by this bound in `call_it_once`
...
LL |     let z = call_it_once(square, 22);
   |                          ^^^^^^ expected an `FnOnce<(&isize,)>` closure, found `for<'r> unsafe fn(&'r isize) -> isize {square}`
   |
   = help: the trait `std::ops::FnOnce<(&isize,)>` is not implemented for `for<'r> unsafe fn(&'r isize) -> isize {square}`

error: aborting due to 5 previous errors

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