1 error[E0282]: type annotations needed
2 --> $DIR/sort_by_key.rs:3:40
4 LL | lst.sort_by_key(|&(v, _)| v.iter().sum());
5 | ^^^ cannot infer type of the type parameter `S` declared on the associated function `sum`
7 help: consider specifying the generic argument
9 LL | lst.sort_by_key(|&(v, _)| v.iter().sum::<S>());
12 error: aborting due to previous error
14 For more information about this error, try `rustc --explain E0282`.