error[E0283]: type annotations needed
  --> $DIR/question-mark-type-infer.rs:12:21
   |
LL |     l.iter().map(f).collect()?
   |                     ^^^^^^^ cannot infer type
   |
   = note: cannot satisfy `_: Try`
   = note: required by `into_result`
help: consider specifying the type argument in the method call
   |
LL |     l.iter().map(f).collect::<B>()?
   |                            ^^^^^

error: aborting due to previous error

For more information about this error, try `rustc --explain E0283`.