Fluent C

Chapter 6. Flexible APIs

Designing interfaces with the right level of flexibility and the right level of abstraction is one of the most important things when writing software, because interfaces represent a contract that often cannot be changed once the system is in operation. Because of this it is important to put stable declarations into the interface and to abstract implementation details, which should have the flexibility to change at a later point in time.

For object-oriented programming languages, you’ll find much guidance on how to design interfaces (for example, in the form of design patterns), but there is not much guidance of this kind for procedural programming languages like C. There are the SOLID design principles (see nearby sidebar) that tell you in general how to design good software. However, for the C programming language, detailed design guidance on how to design interfaces is hard to find, and that’s where the patterns from this chapter come in.

SOLID

The SOLID principles tell us how to implement good, flexible, and maintainable software.

Single-responsibility principle

The code has one responsibility and one reason to be changed in the future.

Open-closed principle

Code should be open for behavior changes without requiring changes to the existing code.

Liskow substitution principle

Codes that implement the same interface should be interchangable for the caller.

Interface segregation principle

Interfaces should be slim and tailored for the caller’s ...