Every Google developer can use any code ever written by the company
Google is unusual in that all software code that underpins its many applications and services is available to every developer at the company. What this means is that anyone can reuse anyone else’s code inside their own application or service.
All software developers use library code, of course: sections of code to do commonly-required things that can be re-used to avoid re-inventing the wheel, and to ensure that things work in a consistent way. But to stretch that approach to literally every piece of code ever written in the company is taking things to a whole new level.
As you might imagine, it’s an approach that’s great for development but a potential nightmare for the upgrades. If your piece of code ends up being used in hundreds or thousands of other applications, what happens when you want to improve it? How do you roll out that improvement to all the other apps relying on it? The answer, of course, is to Google it.
[The] system indexes all Google code, in much the same way Google indexes the web, and then, when an engineer rewrites a library, the system instantly searches the index, locates any software that uses the library, and makes the necessary adjustments. A change made in one place becomes a change made everywhere.
The full article makes interesting reading if you want to see where software development may be headed in the future.