Duck typing

Comparison with other type systems

Structural type systems

Duck typing is similar to, but distinct from, structural typing. Structural typing is a static typing system that determines type compatibility and equivalence by a type's structure, whereas duck typing is dynamic and determines type compatibility by only that part of a type's structure that is accessed during runtime.

The TypeScript, Elm and Python languages support structural typing to varying degrees.

Protocols and interfaces

Protocols and interfaces provide a way to explicitly declare that some methods, operators or behaviors must be defined. If a third-party library implements a class that cannot be modified, a client cannot use an instance of it with an interface unknown to that library even if the class satisfies the interface requirements. A common solution to this problem is the adapter pattern. In contrast, with duck typing, the object would be accepted directly without the need for an adapter.

Templates or generic types

Template (also called generic) functions or methods apply the duck test in a static typing context; this brings all of the advantages and disadvantages of static versus dynamic type checking. Duck typing can also be more flexible in that only the methods actually called at runtime must be implemented, while templates require implementations of all methods that cannot be proven unreachable at compile time.

In languages such as Java, Scala and Objective-C, reflection may be employed to inspect whether objects implement methods or add necessary methods at runtime. For example, Java's MethodHandle API can be used in this manner.