This post is part of an ongoing series on the books that I have read as part of my continual professional development (CPD). All of my CPD posts are available at the following link: Continual Professional Development
In today’s rapidly evolving technology landscape, the ability to build robust, adaptable, and maintainable software is paramount. Not adhering to this approach often leads to a tangled mess of code that’s difficult to understand and maintain. In his book, A Philosophy of Software Design, John K. Ousterhout advocates for a more strategic approach, emphasizing the importance of planning for design improvements. He writes:
If you program strategically, you will continually make small improvements to the system design. This is the opposite of tactical programming, where you are continually adding small bits of complexity that cause problems in the future.
This approach leads to more robust and predictable code, ultimately reducing technical debt and improving long-term project success.
The Importance of Intentional Design
In a fast-paced environment where speed to market is often prioritized, it’s easy to fall into the trap of tactical programming—making quick fixes and adding features without a clear architectural vision. This often leads to a tangled mess of code that’s difficult to understand and maintain. Ousterhout advocates for a more strategic approach, emphasizing the importance of planning for design improvements. He states:
As a software developer, you should always be on the lookout for opportunities to improve the design of the system you are working on, and you should plan on spending some fraction of your time on design improvements.
This isn’t a luxury; it’s an investment in the future stability and scalability of the software. Proactive design reduces rework, improves code quality, and ultimately saves time and resources in the long run.
Design for Maintainability
A well-designed system should be easy to modify and extend. This means minimizing the ripple effect of design changes. Ousterhout highlights the importance of reducing the amount of code affected by each design decision. He explains:
One of the goals of good design is to reduce the amount of code that is affected by each design decision, so design changes don’t require very many code modifications.
This principle is particularly relevant in today’s agile development environments, where changes are frequent. By designing with maintainability in mind, teams can adapt to evolving requirements more efficiently and with less risk. This translates to faster feature delivery, reduced bug fixing time, and a more sustainable development process.
The Power of Abstraction
Abstraction is a fundamental concept in software design, allowing us to hide unnecessary details and focus on the essential aspects of a system. However, poorly designed abstractions can be more harmful than helpful. Ousterhout warns against “false abstractions”: those that omit important details, making the system appear simpler than it actually is. He writes:
An abstraction that omits important details is a false abstraction: it might appear simple, but in reality it isn’t. The key to designing abstractions is to understand what’s important, and to look for designs that minimize the amount of information that is important.
Effective abstraction simplifies the interface and makes the underlying code easier to understand and maintain. Well-crafted abstractions promote code reuse, reduce complexity, and improve overall system clarity.
Prioritising User Experience
Good module design prioritises the needs of its users. This means making the interface as simple and intuitive as possible, even if it requires extra effort on the part of the module designer. Ousterhout argues that a simple interface is more important than a simple implementation. He states:
As a module designer, you should strive to make life as easy as possible for the users of your module, even if that means extra work for you. Another way of expressing this idea is that it is more important for a module to have a simple interface than a simple implementation.
This principle is particularly important for APIs and libraries, where ease of use can significantly impact developer productivity. A user-friendly interface reduces cognitive load, improves developer satisfaction, and ultimately leads to faster and more efficient development.
Clean and Simple Methods
Methods, or functions, should be designed to do one thing and do it well. This principle of single responsibility is essential for creating maintainable and testable code. Ousterhout stresses the importance of clean and simple abstractions in method design. He writes:
When designing methods, the most important goal is to provide clean and simple abstractions. Each method should do one thing and do it completely. The method should have a clean and simple interface, so that users don’t need to have much information in their heads in order to use it.
Well-designed methods make the code easier to understand, test, and reuse. This promotes code clarity, reduces complexity, and improves the overall readability of the codebase.
Error Handling and API Design
Exception handling is often a source of complexity and fragility in software systems. In many cases, exceptions are rare occurrences, and the exception handling code rarely gets executed. When it does, there’s a good chance that it won’t work as intended. Ousterhout highlights the dangers of exception handling, stating: “Code that hasn’t been executed doesn’t work.” He advocates for defining APIs so that there are no exceptions to handle, essentially eliminating the need for exception handling code. He explains:
The best way to eliminate exception handling complexity is to define your APIs so that there are no exceptions to handle: define exceptions out of existence.
This approach leads to more robust and predictable code. By carefully designing APIs to handle potential errors gracefully, developers can avoid the pitfalls of exception handling and create more reliable software.
The Design-It-Twice Approach
Iterative design is a powerful technique for improving software quality. The “design-it-twice” approach involves creating multiple design options and comparing them to identify the best solution. This process not only improves the initial design but also enhances the designer’s skills. Ousterhout writes:
The design-it-twice approach not only improves your designs, but it also improves your design skills. The process of devising and comparing multiple approaches will teach you about the factors that make designs better or worse. Over time, this will make it easier for you to rule out bad designs and hone in on really great ones.
This approach encourages exploration and experimentation, leading to more innovative and effective solutions. By embracing iteration, teams can identify potential problems early on and refine their designs to meet the evolving needs of the project.
Refactoring for Continuous Improvement
Software design is an ongoing process, not a one-time event. As requirements change and new features are added, the system design should evolve accordingly. Ousterhout advocates for refactoring—the process of restructuring existing code without changing its external behaviour—to maintain a clean and maintainable codebase. He states:
Ideally, when you have finished with each change, the system will have the structure it would have had if you had designed it from the start with that change in mind. To achieve this goal, you must resist the temptation to make a quick fix. Instead, think about whether the current system design is still the best one, in light of the desired change. If not, refactor the system so that you end up with the best possible design.
This approach is essential for building sustainable software systems. Regular refactoring helps to prevent code rot, improve code quality, and ensure that the software remains adaptable to future changes
Ready to Transform Your Team?
These are just a few of the many valuable lessons contained within “A Philosophy of Software Design.” I find that these principles are consistently applicable to a wide range of projects and challenges. By embracing simplicity, intentional design, and continuous improvement, teams can build software that is not only functional but also maintainable, scalable, and adaptable to the ever-changing needs of the modern workplace.
If you’re looking to elevate your team’s software development practices and build a more resilient and efficient technology organization, I’d be delighted to discuss how I can help. Reach out today to learn more about my strategic technology consultation services.. I offer tailored guidance to help you navigate the complexities of modern technology and achieve your business goals