error[E0499]: cannot borrow `*self` as mutable more than once at a time --> $DIR/unboxed-closures-recursive-fn-using-fn-mut.rs:22:21 | LL | (self.func)(self, arg) | ----------- ^^^^ second mutable borrow occurs here | | | first mutable borrow occurs here | first borrow later used by call error: aborting due to 1 previous error For more information about this error, try `rustc --explain E0499`.