Glimpse of Google: Code reviews

Welcome to Glimpse of Google, originally a blog series, this insightful collection is now available as a comprehensive eBook. Written by a former Google software engineer, it offers a firsthand look into the inner workings of one of the most transformative companies of our time. This series will uncover how Google operates from an engineering standpoint and explore the broader company culture, guiding principles, and unique approaches that make it a powerhouse in technology. Whether you're an engineer, a tech enthusiast, or simply curious, Glimpse of Google provides insider insights into what makes Google tick.

Code reviews are woven into the very fabric of software development at Google. They understand that even the most brilliant engineer can benefit from another set of eyes. This commitment to quality and shared knowledge drives a meticulous system where every proposed change, no matter how small, undergoes scrutiny before it's integrated into the codebase. Central to this process are two pillars: readability and ownership approvals.

Let's revisit the role of readability approvers. These specialists go beyond understanding a language's syntax; they're champions of its nuances, knowing how to write code that's efficient, easily understood, and maximizes the language's strengths. These experts ensure that proposed changes adhere to these language-specific best practices, raising the quality bar for everyone on the team.

Beyond the technical details, the ownership approval process acts as a safety net. Each section of the codebase is assigned to engineers or teams – those most familiar with how it works and its underlying purpose. When a change touches their domain, an ownership approver steps in. They act as the final line of defense, catching potential issues only someone with deep familiarity of that code would notice. Their review ensures the change doesn't introduce unintended side effects or destabilize delicate interactions with other systems.

But Google takes the process one step further. Even if the change author possesses both readability expertise and ownership rights on that code, a third-party peer review remains mandatory. This underscores a central belief: quality code emerges through collaboration, not isolation.

The benefits extend far beyond catching typos. The act of knowing another engineer will meticulously examine your work fosters a culture of care and attention to detail. Code reviews become a powerful preventative tool, catching errors before they cause problems in production. On a security level, a fresh perspective might reveal vulnerabilities the original author overlooked, leading to pre-emptive mitigation rather than frantic bug fixes later on.

The review process is itself a dynamic learning experience. Reviewers don't hold a monopoly on knowledge – their comments, questions, and suggestions often spark discussions that benefit both parties. For junior engineers, reviews are an invaluable way to absorb best practices and understand how to craft elegant solutions. Experienced engineers hone their skills as mentors, sharing their wisdom and ensuring a consistent standard of quality. This respectful exchange of ideas is a hallmark of Google's approach, transforming code reviews from a chore into an opportunity for collaborative growth.

A key principle here is that code should be primarily readable by humans, not just machines. While computers can execute any valid code, it's the human engineers who need to understand, maintain, and enhance it over time. This process ensure that proposed changes are comprehensible by the team and not just the author of the change.

Of course, it takes more than just checking a box. Code reviews require engineers to master the art of providing constructive feedback and gracefully receiving criticism. Respectful communication ensures the process focuses on improving the code rather than undermining confidence. Finally, the cycle of review isn't truly complete until the original author has meticulously addressed the reviewer's comments. This may require multiple iterations, with the reviewer acting as a guide until they are confident the change is ready to become part of the larger system.

Code reviews at Google are about more than just correctness. They embody a deep commitment to software that is not just functional but also maintainable, secure, and designed to evolve gracefully alongside user needs.