Isinstancevalue

Isinstancevalue is a programming utility concept used to determine whether a given value satisfies a specified type constraint. The term appears in discussions of dynamic typing and type checking and may be described in documentation or proposals for hypothetical libraries or languages. In its common framing, it yields a boolean result indicating whether the value is considered an instance of the requested type or types.

A typical usage pattern involves a function or API call such as isinstancevalue(value, type_or_types). For example, isinstancevalue(5, int) would return true, and isinstancevalue(obj, (A, B)) would return true when obj is an instance of A or B. Some designs also allow optional flags to require exact type matches instead of subclass checks, or to enable structural checks that verify the presence of certain attributes or methods in addition to nominal type membership.

Relation to the built-in isinstance is central. While isinstance is strictly class-based in many languages, isinstancevalue is often discussed as potentially extending or complementing such checks with additional semantics, such as structural or protocol-based conformance, richer error reporting, or compatibility with duck typing. In practice, proponents argue that a more expressive predicate can simplify validation logic, while critics note the potential for increased runtime overhead and design fragility.

Limitations include reliance on runtime type information and possible conflicts with dynamic or polymorphic programming styles. Alternatives include traditional isinstance checks, type predicates, or explicit protocol and interface checks. See also: isinstance, type checking, duck typing.