Casedispatch

Casedispatch refers to a mechanism for selecting and invoking a function or operation based on the value of a designated case or discriminant within a program. It is a general form of dispatch that contrasts with solely type-based or method-based dispatch by choosing behavior according to the actual case label, key, or pattern present at runtime.

Typical implementations rely on a dispatch table or switch-like construct. In a dispatch table, a map from case labels to handler functions is kept, allowing a lookup to yield the appropriate action in constant or near-constant time. Alternatives include chained conditional branches or pattern-matching constructs that decompose the input and route execution accordingly. In dynamic languages, case-based dispatch can be implemented with dictionaries or maps from keys to callable handlers; in static languages, features like switch statements or pattern matching serve a similar role.

Usage scenarios include command processing, protocol or file format handling, and event-driven systems where different inputs or events require distinct processing logic. Casedispatch supports modularity by decoupling the decision logic from the execution routines, making it easier to add or modify cases without altering core control flow.

Advantages of casedispatch include simpler extension of behavior, clearer separation of concerns, and potential performance benefits from table-based dispatch. Limitations can arise as the number of cases grows, increasing maintenance complexity, or when cases share common setup code, leading to duplication unless shared abstractions are used. Casedispatch is related to but distinct from type-based polymorphism, multimethods, and pattern matching.