Elixir Patterns

Prescriptive. Follow these when writing Elixir code.

A pattern is a reusable solution to a recurring problem. Each one has:

• When to use — the problem it solves
• When NOT to use — where it causes harm
• Why — the reasoning, not just the rule
• Source citations — verified file:line from real codebases

These are derived from what mature Elixir codebases actually do, not opinions or blog posts.

Structure

• patterns/ — what to do (behaviours, GenServer, error handling, testing, typespecs, etc.)
• smells/ — what NOT to do (anti-patterns, common mistakes)
• sources/ — reference material from specific projects (Oban, elixir-lang). Study for ideas, don't copy blindly.

How to use

Writing code

Read the relevant pattern files from this repo before writing code. Your implementation must follow the documented patterns — if you deviate, justify why in a comment. Check smells/ to make sure you're not introducing a known anti-pattern.

Reviewing code

Read the relevant pattern files from this repo. For each function or module in the diff, verify it follows the documented pattern. If the code deviates, flag it with a reference to the specific pattern and section. A deviation without justification is a finding.

Evaluating a pattern

Read the pattern file. Compare against how the following projects handle the same problem: [list projects]. Does the pattern hold? Are there cases where it breaks down? Update the pattern with what you find.

Patterns vs Conventions

Pattern = prescriptive. "When you face X, do Y." Language-scoped. Follow these.

Convention = descriptive. "Project Z does it this way." Context-specific. Study for ideas — applying another project's conventions to yours without understanding their constraints causes harm.

The sources/ directory is convention material absorbed from thin repos. The patterns/ directory is what you actually follow.