type erasure

Hiding a value's real type behind a trait.

Type erasure stores a value as a trait object (Box) so code can hold many types uniformly but can no longer see which one it has without downcasting.

Examples

let e: Box<dyn Error> = "x".parse::<u32>().unwrap_err().into(); no longer shows it is a ParseIntError, but e.downcast_ref::<ParseIntError>() returns Some.