# Mutable data

> 코드 악취 중 하나.

[코드 악취](https://wiki.g15e.com/pages/Code%20smell.txt) 중 하나.

## 관련 리팩토링

- <Encapsulate variable>
- <Split variable>
- <Slide statements>
- <Extract function>
- <Separate query from modifier>
- <Remove setting method>
- <Replace derived variable with query>
- <Combine functions into class>
- <Combine functions into transform>
- <Change reference to value>

## 함수형 프로그래밍

변하는 데이터 그 자체를 문제의 원인으로 보는 접근:

> For this reason, an entire school of software development—[functional programming](https://wiki.g15e.com/pages/Functional%20programming.txt)—is based on the notion that data should never change and that updating a data structure should always return a new copy of the structure with the change, leaving the old data pristine. --Chapter 3, [Refactoring: Improving the design of existing code](https://wiki.g15e.com/pages/Refactoring%20-%20Improving%20the%20design%20of%20existing%20code.txt)

(모든 함수형 프로그래밍이 변수를 허용하지 않는 건 아니다.)