error[E0038]: the trait `Expr` cannot be made into an object --> $DIR/object-safety-issue-22040.rs:12:23 | LL | trait Expr: Debug + PartialEq { | ---- --------- ...because it uses `Self` as a type parameter in this | | | this trait cannot be made into an object... ... LL | elements: Vec>, | ^^^^^^^^^^^^^ the trait `Expr` cannot be made into an object error: aborting due to previous error For more information about this error, try `rustc --explain E0038`.