mostderived

Mostderived is a term used in computer science to describe the most-derived type within a set of related types—that is, the most specific subtype that remains a common subtype of all members of the set. The concept is frequently discussed in the context of type resolution, dynamic casting, and method lookup in languages that support inheritance or polymorphism.

Formal definition: Given a collection T of types, a type D is most-derived for T if D is a subtype of every type in T, and for any other type E that is also a subtype of every type in T, E is a supertype of D. In practice, not every collection of types has a most-derived type; when two or more subtypes are incomparable or no single subtype is contained in all members of T, a most-derived type does not exist.

Applications: The notion informs decisions about resolving casts or selecting a common interface in languages with multiple inheritance or rich type systems. It can guide dynamic binding, reflection, and serialization workflows by identifying the most specific shared type to operate on, or by determining a safe default downcast before applying type-specific logic.

Relation to related concepts: Mostderived is related to the least upper bound (or join) in type lattices, common supertypes, and the notion of a most specific common subtype. It contrasts with cases where a common base type exists but no single most-derived type can be identified.

Caveats: The term is not uniformly standardized across programming communities. Some discussions prefer “most-derived common type” or “most specific common subtype,” and in certain languages the practical mechanism for resolving such a type may depend on the language’s inheritance and method resolution rules.