1 error[E0308]: mismatched types
2 --> $DIR/occurs-check.rs:5:9
5 | ^^^^^ cyclic type of infinite size
7 help: try using a conversion method
9 LL | f = (box f).to_string();
12 error: aborting due to previous error
14 For more information about this error, try `rustc --explain E0308`.