Comment by zozbot234

> it can be always replaced with composition, which Rust already supports

Strictly speaking, open recursion (a notorious footgun in implementation inheritance, and arguably the underlying cause of the "fragile base class" problem) cannot be implemented via composition as-is. You need a complex "tie-the-knot" construction, typing "self" as an existential type defined in terms of itself, to enforce an indirection through the object's vtable in all calls to overridable methods. (AIUI, Rust does not have existential types that are general enough to allow this, albeit that might happen at some point as part of overall improvements to the type system.)