The Expression Problem and its solutions
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, as adding operations requires modifying existing interfaces and classes.
- Functional programming (FP) makes it easy to add new operations but difficult to add new types, as adding types requires modifying existing functions to handle the new type.
- The visitor pattern in OOP can 'flip' the problem, making it easier to add operations but harder to add types, by deferring computation to visitor classes.
- 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 enable adding new operations (protocols) and new types (records) dynamically, solving the expression problem by keeping interfaces minimal and extensible.
- Multiple dispatch and open methods in languages like Clojure allow methods to be defined outside types, enabling flexible extension without source code modification.
- The expression problem highlights the trade-offs between OOP and FP, emphasizing the need for language features that support both extensibility and maintainability.