Circular References

Circular references manifest when two or more entities—whether they be functions, modules, or data structures—depend on each other either directly or indirectly, thus creating a loop of dependencies. This phenomenon is particularly noticeable in procedural programming, where the flow of execution revolves around procedures or functions and modules that contain related functions. At a higher level, they can manifest between libraries or projects, where one library depends on another, which in turn depends on the first. This kind of circularity at the library or project level can pose significant challenges for building, maintaining, and deploying software.

Why circular references should be avoided

  1. Initialization issues: In procedural systems, the sequence of operations matters immensely. Circular dependencies can create ambiguity in the sequence in which functions or modules should be executed. If function A relies on function B, but function B in some way relies on A, then deciding which to run first becomes a challenge.

  2. Maintenance difficulty: Code with circular references tends to be more intricate and harder to decipher. If you change one function that’s part of a circular dependency, it’s easy to inadvertently affect others in the loop, potentially introducing unforeseen bugs.

  3. Build and deployment challenges: When two libraries reference each other, building or deploying them in isolation becomes problematic. Determining which library should be built, tested, or deployed first is ambiguous when each relies on the other.

  4. Tight coupling: This is a core concern with circular references. Tight coupling refers to when different parts of a program are interdependent, making them reliant on each other’s detailed implementation. The dangers of tight coupling include

    • Reduced flexibility: Changes in one function might necessitate changes in another due to their close interdependence.
    • Reduced readability: New developers or even the original programmers might find it difficult to understand the flow and logic of tightly coupled code, especially after some time has passed.
    • Reduced reusability: When functions are tightly coupled, extracting one for use in a different context becomes challenging since it’s intertwined with other functions.
    • Increased fragility: A change or a bug in one function can have cascading effects throughout the system, making the program more prone to errors and harder to debug.

Techniques to refactor circular references in procedural code

  1. Reorder operations: Evaluate if the operations in the dependent functions can be reordered to break the cycle. Sometimes, resequencing tasks within functions can prevent the need for cyclic calls.

  2. Pass data instead of making calls: If one function is calling another just to get some data, consider if that data can be calculated beforehand and passed as an argument instead.

  3. Restructure libraries or modules: Whether dealing with intricate operations in procedural code or dependencies between libraries, extracting the common elements causing circularity can be a strategic move. By isolating these elements into separate helper functions, utility modules, or shared components, multiple functions or libraries can then reference this central entity. This approach not only breaks the circular dependencies but also emphasizes a reliance on shared abstractions or utilities rather than direct, intertwined dependencies.

  4. Dependency inversion: Instead of one library depending on another, both libraries can be made to depend on a third abstraction or a shared component. This inverts the dependencies, ensuring that higher-level libraries are not dependent on lower-level details but rather on abstractions.

  5. Reevaluate design decisions: At both the procedural and library levels, circular references often hint at underlying design issues. Whether it’s the architecture, responsibilities, relationships of components, or the logic flow within a program, such circularities may indicate the need for a design review. Revisiting the overall structure, architecture, and design of the system can help identify and implement more linear or hierarchical structures, ensuring smoother operations and reducing dependencies.