error[E0282]: type annotations needed
  --> $DIR/type-annotations-needed-expr.rs:2:39
   |
LL |     let _ = (vec![1,2,3]).into_iter().sum() as f64;
   |                                       ^^^
   |                                       |
   |                                       cannot infer type for `S`
   |                                       help: consider specifying the type argument in the method call: `sum::<S>`
   |
   = note: type must be known at this point

error: aborting due to previous error

For more information about this error, try `rustc --explain E0282`.