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skills/refactoring-safely/resources/refactoring-patterns.md

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+## Common Refactoring Patterns
+
+### Extract Method
+
+**When:** Duplicated code or long function
+
+```rust
+// Before: Long function
+fn process(data: Vec<i32>) -> i32 {
+    let mut sum = 0;
+    for x in data {
+        sum += x * x;
+    }
+    sum
+}
+
+// After: Extracted method
+fn process(data: Vec<i32>) -> i32 {
+    data.iter().map(|x| square(x)).sum()
+}
+
+fn square(x: &i32) -> i32 {
+    x * x
+}
+```
+
+**Steps:**
+1. Extract square() function
+2. Run tests
+3. Commit
+4. Replace loop with iterator
+5. Run tests
+6. Commit
+
+### Rename Variable/Function
+
+**When:** Name is unclear or misleading
+
+```rust
+// Before
+fn calc(d: Vec<i32>) -> f64 {
+    let s: i32 = d.iter().sum();
+    s as f64 / d.len() as f64
+}
+
+// After - Step by step
+// Step 1: Rename function
+fn calculate_average(d: Vec<i32>) -> f64 { ... }  // Test, commit
+
+// Step 2: Rename parameter
+fn calculate_average(data: Vec<i32>) -> f64 { ... }  // Test, commit
+
+// Step 3: Rename variable
+fn calculate_average(data: Vec<i32>) -> f64 {
+    let sum: i32 = data.iter().sum();  // Test, commit
+    sum as f64 / data.len() as f64
+}
+```
+
+### Extract Class/Struct
+
+**When:** Class has multiple responsibilities
+
+```rust
+// Before: God object
+struct UserService {
+    db: Database,
+    email_validator: Regex,
+    name_validator: Regex,
+}
+
+// After: Single responsibility
+struct UserService {
+    db: Database,
+    validator: UserValidator,  // EXTRACTED
+}
+
+struct UserValidator {
+    email_pattern: Regex,
+    name_pattern: Regex,
+}
+```
+
+**Steps:**
+1. Create empty UserValidator struct
+2. Test, commit
+3. Move email_validator field
+4. Test, commit
+5. Move name_validator field
+6. Test, commit
+7. Update UserService to use UserValidator
+8. Test, commit
+
+### Inline Unnecessary Abstraction
+
+**When:** Abstraction adds no value
+
+```rust
+// Before: Pointless wrapper
+fn get_user_email(user: &User) -> &str {
+    &user.email
+}
+
+fn process() {
+    let email = get_user_email(&user);  // Just use user.email!
+}
+
+// After: Inline
+fn process() {
+    let email = &user.email;
+}
+```
+
+**Steps:**
+1. Replace one call site with direct access
+2. Test, commit
+3. Replace next call site
+4. Test, commit
+5. Remove wrapper function
+6. Test, commit
+