functional-programming

To isolate side effects and improve purity, you refactor code by extracting business logic into pure functions and moving I/O operations to the boundaries of your system. This creates a predictable pure core and an imperative shell for side-effect management.

The best way to enforce immutability and prevent race conditions in TypeScript or PHP is to refactor mutable state into immutable data structures. This simplifies reasoning about state and removes unexpected mutations, making the code more robust and testable.

Mixing business logic with database writes causes bugs because impure functions rely on and modify external state, creating unpredictable side effects. Isolating these side effects to the system boundaries makes the core logic predictable and reduces state-related bugs.

Yes, you can refactor complex order processing functions by applying functional programming principles. This separates the mixed business logic and external API calls into a pure core function and an imperative shell that handles the side effects, improving overall code quality.

You should not use functional programming refactoring when your codebase heavily relies on mutable state and imperative loops that cannot be isolated, or when isolating side effects to the boundaries is architecturally unfeasible without a complete system rewrite.