500lines

500 Lines or Less is the source repository for a programming book of the same name, the fourth volume in the Architecture of Open Source Applications series. The book takes a different approach from most programming tutorials: instead of teaching syntax or introducing frameworks, it explains how experienced programmers think about design decisions — why they split code into particular modules, when to use inheritance versus composition (two ways of organizing code), and how to anticipate future changes.

Each chapter is a walkthrough of a small, self-contained program — no more than 500 lines of code — that solves a classic software engineering problem. Examples include a web crawler, a spreadsheet, a static analysis tool, an object model, and a pedometer. Each program was written by a different experienced contributor who explains the thinking behind the design choices made along the way.

The book is part of a series aimed at helping programmers understand how well-known types of software are actually built. All written content is under a Creative Commons license (free to share with attribution for non-commercial use), and all code is under the MIT license. Someone would read this to develop better intuitions about software architecture and design at a scale they can fully grasp and study.