error[E0282]: type annotations needed for `RaceBuilder>` --> $DIR/issue-84073.rs:32:16 | LL | Race::new(|race| race.when()); | ^^^^ ---- type must be known at this point | help: consider giving this closure parameter an explicit type, where the type for type parameter `T` is specified | LL | Race::new(|race: RaceBuilder>| race.when()); | ++++++++++++++++++++++++++ error: aborting due to 1 previous error For more information about this error, try `rustc --explain E0282`.