Clean Code – Chapter 6 Objects and Data Structures-优快云博客

本文详细解读了代码重构中至关重要的笛米特法则，通过实例展示了如何遵循这一原则来优化代码结构，减少耦合度，提高代码的可维护性和可扩展性。介绍了数据抽象、隐藏实现、面向对象的特性以及Procedural和OO编程风格的差异，特别强调了在添加新功能或数据结构时应遵循的原则。

Data Abstraction

Hiding implementation
Data/Object Anti-Symmetry

Objects hide their data behind abstractions and expose function that operate on that data. Data structure expose their data and hava no meaningful functions.

Procedural code(code using data structure) makes it easy to add new functions without changing the existing data structures. OO code, on the other hand, makes it easy to add new classes without changing existing functions.

Procedural code makes it hard to add new data structures because all functions must change. OO code makes it hard to add new functions because all the classes must change.
The Law of Demeter

A module should not know about the innards of the objects it manipulates.

A method f of a class C should only call the methods of these:
- C
- An object created by f
- An object passed as an argument to f
- An object held in an instance variable of C
推荐一篇博文：笛米特法则详解，通过一个简单的代码示例解释了上述概念。
- Train Wrecks
  
  Bad code:
```
final String outputDir = ctxt.getOptions().getScratchDir().getAbsolutePath();
```
  Or
```
Options opts = ctxt.getOptions();
File scratchDir = opts.getScratchDir();
final String outputDir = scratchDir.getAbsolutePath();
```
  Only used for data structures
```
final String outputDir = ctxt.options.scratchDir.absolutePath;
```
- Hybrids
  
  Avoid hybrid structures that are half object and half data structure.
- Hiding Structure
  
  Tell an object to do something, not ask it about its internals.
Data Transfer Objects (DTO)

The quintessential form of a data structure is a class with public variables and no functions.
- Active Record
  
  Special form of DTO. Hava navigational methods like save and find.
  
  Typically direct translations from database tables, or other data sources.