The Expression Problem and its solution
3 days ago
- #programming
- #Clojure
- #design-patterns
- The expression problem is a fundamental software design issue where adding both new data types and new operations to an existing system is challenging without modifying existing code.
- Object-oriented programming (OOP) makes it easy to add new types but difficult to add new operations, requiring changes to existing interfaces and classes.
- Functional programming (FP) makes it easy to add new operations but difficult to add new types, requiring updates to all existing functions handling those types.
- The visitor pattern in OOP can 'flip' the problem, making it easier to add operations but harder to add types, though it introduces complexity and limitations.
- Clojure's multimethods and protocols provide elegant solutions to the expression problem by allowing independent extension of types and operations without modifying existing code.
- Clojure's protocols, similar to interfaces, enable types to implement operations after their definition, supporting extensibility without source code access.
- Multiple dispatch and open methods in languages like Clojure allow methods to be defined outside types, facilitating clean solutions to the expression problem.
- Small, single-method protocols are recommended for better extensibility, as adding methods to existing protocols is problematic.