coding-standards

Coding Standards

D9 Canonical Reference. This is the single source of truth for cross-language coding standards. Language-specific reviewers (@typescript-reviewer, @python-reviewer, etc.) embed these rules. Agents cite this skill as "See also: /coding-standards."

Naming Conventions

Variables & Functions

Language	Variables	Functions	Constants
TypeScript / JavaScript	camelCase	camelCase	SCREAMING_SNAKE_CASE
Python	snake_case	snake_case	SCREAMING_SNAKE_CASE
Go	camelCase	camelCase	CamelCase (exported)
Rust	snake_case	snake_case	SCREAMING_SNAKE_CASE
Java	camelCase	camelCase	SCREAMING_SNAKE_CASE
C#	camelCase	PascalCase	PascalCase
Swift	camelCase	camelCase	camelCase

Classes / Types / Interfaces

PascalCase — all languages, no exceptions.

Booleans

Prefix with is, has, can, should: isLoading, hasError, canEdit, shouldRefresh.

Collections

Plural nouns: users, errors, items — not userList, errorArray.

Avoid

• Single-letter variables outside loop counters (i, j, k are OK in loops)
• Abbreviations that save under 3 characters: usr → user, mgr → manager
• Redundant type names: UserInterface, UserClass, UserObject → just User

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Function Design

• Max length: 50 lines (firm guideline; > 80 lines is always a split target)
• Single responsibility: one function, one job — if "and" appears in the description, split it
• Max parameters: 3; beyond that, use an options/config object
• Cyclomatic complexity: ≤ 10; > 15 is a mandatory refactor target
• Nesting depth: ≤ 3 levels; use early returns to flatten

Early Return Pattern (preferred)

// BEFORE — deep nesting
function handle(input) {
  if (input) {
    if (input.valid) {
      return process(input);
    }
  }
  return null;
}

// AFTER — early returns
function handle(input) {
  if (!input || !input.valid) return null;
  return process(input);
}