error[E0277]: expected a `Fn<(&isize,)>` closure, found `for<'a> extern "C" fn(&'a isize) -> isize {square}` --> $DIR/unboxed-closures-wrong-abi.rs:20:21 | LL | let x = call_it(&square, 22); | ------- ^^^^^^^ expected an `Fn<(&isize,)>` closure, found `for<'a> extern "C" fn(&'a isize) -> isize {square}` | | | required by a bound introduced by this call | = help: the trait `for<'a> Fn<(&'a isize,)>` is not implemented for fn item `for<'a> extern "C" fn(&'a isize) -> isize {square}` note: required by a bound in `call_it` --> $DIR/unboxed-closures-wrong-abi.rs:9:15 | LL | fn call_it isize>(_: &F, _: isize) -> isize { | ^^^^^^^^^^^^^^^^^^^ required by this bound in `call_it` error[E0277]: expected a `FnMut<(&isize,)>` closure, found `for<'a> extern "C" fn(&'a isize) -> isize {square}` --> $DIR/unboxed-closures-wrong-abi.rs:25:25 | LL | let y = call_it_mut(&mut square, 22); | ----------- ^^^^^^^^^^^ expected an `FnMut<(&isize,)>` closure, found `for<'a> extern "C" fn(&'a isize) -> isize {square}` | | | required by a bound introduced by this call | = help: the trait `for<'a> FnMut<(&'a isize,)>` is not implemented for fn item `for<'a> extern "C" fn(&'a isize) -> isize {square}` note: required by a bound in `call_it_mut` --> $DIR/unboxed-closures-wrong-abi.rs:12:19 | LL | fn call_it_mut isize>(_: &mut F, _: isize) -> isize { | ^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `call_it_mut` error[E0277]: expected a `FnOnce<(&isize,)>` closure, found `for<'a> extern "C" fn(&'a isize) -> isize {square}` --> $DIR/unboxed-closures-wrong-abi.rs:30:26 | LL | let z = call_it_once(square, 22); | ------------ ^^^^^^ expected an `FnOnce<(&isize,)>` closure, found `for<'a> extern "C" fn(&'a isize) -> isize {square}` | | | required by a bound introduced by this call | = help: the trait `for<'a> FnOnce<(&'a isize,)>` is not implemented for fn item `for<'a> extern "C" fn(&'a isize) -> isize {square}` note: required by a bound in `call_it_once` --> $DIR/unboxed-closures-wrong-abi.rs:15:20 | LL | fn call_it_once isize>(_: F, _: isize) -> isize { | ^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `call_it_once` error: aborting due to 3 previous errors For more information about this error, try `rustc --explain E0277`.