A Philosophy of Software Design

Table of contents

Introduction

In an effort to improve my development skills, I recently finished reading John Ousterhout’s book “A Philosophy of Software Design.” Here are the five main takeaways that I decided to keep.

1. Reducing Complexity

Complexity is the Primary Enemy

The primary enemy of any software designer is complexity. The main goal of a project or team of programmers is to reduce complexity by writing simple, effective, and clear code.

Code Clarity Over Performance

Performance is important, but code clarity wins in the long term. Code clarity means how predictable a module is, making it easier for a developer to understand and expand it without much effort. A performant module is important, but if it is not predictable, it becomes difficult for developers to maintain, expand, or modify. Clear code is easier to understand and maintain, and performance issues can often be addressed later if they become problematic.

2. Module Design and Interfaces

According to the author, it’s important for modules to have the following characteristics:

Deep Modules

A module has depth when the module logic is pushed below the interfaces that expose that logic. John Ousterhout believes developers should strive to create modules with simple interfaces that provide significant functionality. The implementation should be hidden in deeper layers of the code, avoiding business logic in the interfaces.

General-Purpose Modules

Modules should be designed with reusability in mind. Developers should aim to create general-purpose modules.

Simple and Evolving Interfaces

Interfaces should be as simple as possible to be understandable, increasing code clarity. Additionally, interfaces should be designed to evolve, and deep modules allow interfaces to be both simple and adaptable.

3. Consistency and Clarity

Code consistency and clarity help the codebase evolve smoothly.

Consistency

Consistent design decisions reduce complexity and increase the clarity and predictability of the codebase. This makes code changes easier and the code more maintainable.

Comments and Naming

Developers should follow best practices when writing comments. It is important to write clear comments without overdoing it. Describe complicated parts of the codebase and use clear documentation generators to describe the functionalities of functions and interfaces.

Choosing descriptive names for variables and functions provides important context, reducing the need for comments in certain parts of the codebase.

Documentation

Maintaining good documentation that explains the design and rationale of the code is crucial for long-term maintenance. Keeping documentation close to the code ensures it is easily accessible and more likely to be updated alongside the code. Documentation should explain the “why” and the “how” of the code, helping future developers understand the rationale behind decisions. Providing examples and use cases illustrates how the code can be used, making it easier to understand and apply in different contexts.

4. Development Practices

The book also provides tips on best development practices in the long term.

Incremental Development

Software should be developed incrementally, ensuring that changes and improvements are small enough to be manageable. This allows developers to maintain control and consistency with the rest of the codebase.

Testing and Refactoring

Software should be thoroughly tested and regularly refactored to keep the code clean and maintainable.

5. Pragmatism and Adaptability

Two characteristics of good software design are pragmatism and adaptability. Since software inevitably changes, developers should be pragmatic, realistic, and ready to adapt.

Design for Change

Changes should be expected, and good developers should plan for them. Practices such as code clarity, general-purpose modules, code consistency, and testing help prepare the code for change.

Pragmatism

Software engineers should be pragmatic when making design decisions. Practical compromises must be made, balancing trade-offs, analyzing constraints, and focusing on the value provided.

Error Handling

Errors should be handled gracefully. Error handling should be as simple and clear as possible, as complex error handling logic can introduce additional bugs and make the code harder to understand and maintain. Keeping error handling centralized can simplify the codebase and make it easier to manage. This involves having a common mechanism for dealing with errors, rather than scattering error handling code throughout the application.