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skills/ln-341-code-quality-checker/references/yagni_violations.md

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+# YAGNI Violations Reference
+
+YAGNI (You Aren't Gonna Need It) principle: Don't add functionality until it's necessary.
+
+## Violation Patterns
+
+### 1. Unused Functions/Classes
+
+**Violation:**
+```python
+def calculate_tax(amount):  # Defined but never called!
+    return amount * 0.2
+
+def process_payment(amount):
+    return charge_card(amount)  # Doesn't use calculate_tax
+```
+
+**Detection:** Search codebase for function calls; if function never called → YAGNI violation
+
+---
+
+### 2. Premature Abstraction
+
+**Violation:**
+```python
+# Interface with only ONE implementation
+class UserRepositoryInterface:
+    def get_user(self, id): pass
+    def save_user(self, user): pass
+
+class UserRepository(UserRepositoryInterface):  # Only implementation!
+    def get_user(self, id):
+        return db.query(User).get(id)
+    def save_user(self, user):
+        db.session.add(user)
+        db.session.commit()
+```
+
+**Fix:** Remove interface until second implementation needed
+
+---
+
+### 3. Over-Engineering
+
+**Violation:**
+```python
+# Complex pattern for simple problem
+class UserFactoryBuilder:
+    def __init__(self):
+        self.strategy = None
+
+    def set_strategy(self, strategy):
+        self.strategy = strategy
+        return self
+
+    def build(self):
+        return User(strategy=self.strategy)
+
+# Usage
+user = UserFactoryBuilder().set_strategy('default').build()
+```
+
+**Fix:**
+```python
+# Simple solution
+user = User()
+```
+
+---
+
+**Version:** 1.0.0
+**Last Updated:** 2025-11-13