---
title: "Coding Style"
description: "ALWAYS create new objects, NEVER mutate existing ones:"
type: skill
canonical_url: https://claudary.paisolsolutions.com/skills/coding-style-1
source: "Claudary"
difficulty: intermediate
author: "Claude Code Knowledge Pack"
date: 2026-07-10T11:14:15.856Z
license: CC-BY-4.0
attribution: "Coding Style — Claudary (https://claudary.paisolsolutions.com/skills/coding-style-1)"
---

# Coding Style
ALWAYS create new objects, NEVER mutate existing ones:

## Overview

---
inclusion: auto
description: Core coding style rules including immutability, file organization, error handling, and code quality standards.
---

# Coding Style

## Immutability (CRITICAL)

ALWAYS create new objects, NEVER mutate existing ones:

```
// Pseudocode
WRONG:  modify(original, field, value) → changes original in-place
CORRECT: update(original, field, value) → returns new copy with change
```

Rationale: Immutable data prevents hidden side effects, makes debugging easier, and enables safe concurrency.

## File Organization

MANY SMALL FILES > FEW LARGE FILES:
- High cohesion, low coupling
- 200-400 lines typical, 800 max
- Extract utilities from large modules
- Organize by feature/domain, not by type

## Error Handling

ALWAYS handle errors comprehensively:
- Handle errors explicitly at every level
- Provide user-friendly error messages in UI-facing code
- Log detailed error context on the server side
- Never silently swallow errors

## Input Validation

ALWAYS validate at system boundaries:
- Validate all user input before processing
- Use schema-based validation where available
- Fail fast with clear error messages
- Never trust external data (API responses, user input, file content)

## Code Quality Checklist

Before marking work complete:
- [ ] Code is readable and well-named
- [ ] Functions are small (<50 lines)
- [ ] Files are focused (<800 lines)
- [ ] No deep nesting (>4 levels)
- [ ] Proper error handling
- [ ] No hardcoded values (use constants or config)
- [ ] No mutation (immutable patterns used)

---

Source: [Claudary](https://claudary.paisolsolutions.com/skills/coding-style-1) · https://claudary.paisolsolutions.com