DRY

Don’t Repeat Yourself.

• Logical duplication: Solving by abstracting into a more fine-grained function.

  For example: Both isValidUsername() and isValidPassword() can use the fine-grained function canContain().

• Functional semantic duplication: Solving by removing the duplicated function.

• Duplicate code execution: Solving by removing the duplicated execution.

Code Reusability

When we develop new features, we try to reuse existing code as much as possible.

The difference between reusability and not duplication is that "not duplication" doesn't make sure reusability.

To improve the code reusability:

• decouple the codes

• use single responsibility principle

• encapsulate into modules

• split bussiness and non-bussiness logic

• put the generic codes to lower layer, avoid the low layer class to use high layer class.

• use OOP and design pattern

However, Code Reusability costs time to design. We can apply the rule of three:

When we write the code for the first time, we don’t consider reusability. When we encounter the reuse scene for the second time, we refactor to make it reuse.