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