isinstanceobj

isinstanceobj is a hypothetical utility in dynamic programming environments designed to determine whether a given object conforms to a specified type descriptor. Unlike conventional type checks that rely solely on a fixed class or inheritance hierarchy, isinstanceobj aims to support both nominal and structural type validation, enabling checks against interfaces and inferred capabilities as well as concrete classes.

A type descriptor for isinstanceobj can take several forms. It may be a single class or a tuple of classes, mirroring traditional type semantics. It can also be a string identifier for a named type, an interface descriptor that lists required members, or a predicate function that programmatically inspects the object. When a structural or interface descriptor is used, the function verifies that the object exposes the required attributes or methods, and may optionally verify method signatures.

In practice, isinstanceobj is used to enforce API contracts, perform input validation, or implement dynamic dispatch where the exact runtime type is less important than the object's capabilities. It can also support a strict mode, which requires exact type equality rather than subclass relationships, or a non-strict mode, which permits subclass instances to pass the check.

Implementation considerations include performance impact of structural checks, the potential for false positives if capabilities are not well defined, and interactions with static type hints or runtime reflection. Different language ecosystems may implement different variants with varying semantics and naming.

See also: isinstance, type checking, duck typing, structural typing, interface checkers.