error[E0782]: expected a type, found a trait --> src/main.rs:1:23 | 1 | fn foo(x: u32) -> Box<Fn(u32) -> u32> { | ^^^^^^^^^^^^^^ | help: you can add the `dyn` keyword if you want a trait object | 1 | fn foo(x: u32) -> Box<dyn Fn(u32) -> u32> { | +++ For more information about this error, try `rustc --explain E0782`.

error[E0373]: closure may outlive the current function, but it borrows `x`, which is owned by the current function --> src/main.rs:2:14 | 2 | Box::new(|y| x + y) | ^^^ - `x` is borrowed here | | | may outlive borrowed value `x` | note: closure is returned here --> src/main.rs:2:5 | 2 | Box::new(|y| x + y) | ^^^^^^^^^^^^^^^^^^^ help: to force the closure to take ownership of `x` (and any other referenced variables), use the `move` keyword | 2 | Box::new(move |y| x + y) | ++++ For more information about this error, try `rustc --explain E0373`.

rustc 1.85.0 (4d91de4e4 2025-02-17) binary: rustc commit-hash: 4d91de4e48198da2e33413efdcd9cd2cc0c46688 commit-date: 2025-02-17 host: x86_64-unknown-linux-gnu release: 1.85.0 LLVM version: 19.1.7