roam/20201008164835-structural_typing.org

Structural Typing

A structural type system (or property-based type system) is a major class of Type System in which type compatibility and equivalence are determined by the type's actual structure or definition and not by other characteristics such as its name or place of declaration. Structural systems are used to determine if types are equivalent and whether a type is a subtype of another.

— https://en.wikipedia.org/wiki/Structural_type_system

Structural type systems can achieve static Duck Typing, in that a type's structure is what determines its suitability, not its name.