# iv - 3

## Clean Code

### software = build a house

1. basic = building plan.
2. build different purpose: apartment, hotel, business, etc.
3. goal: build house, and make customer happy.

TDD = possible to optimize parts of codes, not full redo.

## OOP

`inheritance, encapsulation, polymorphism`

#### Inheritance

mixin = multiple inheritance

put common methods, attributes to ancestor

#### Encapsulation

1. restricting direct access to some

```cpp
class Base {
    public:
        int publicMember;
    protected:
        int protectedMember;
    private:
        int privateMember;
};
```

* Everything that is aware of Base is also aware that Base contains publicMember.
* Only the children (and their children) are aware that Base contains protectedMember.
* No one but Base is aware of privateMember.

#### Polymorphism

* Different vendors design chips base on the same interface.
* interface = every animal has `eat()` **method**, no matter it is mammal or insect.

### Overload & override

overload = same scope, run-time-polymorphism

override = inheritance, same signature, compile-time-polymorphism

## FP

#### pure function, declarative, higher order function

immutable variable = no variable lock, and you will not encounter deadlock. = No wife, no divorce.

declarative = what to do, not how to do.

hof = input fn as params and output params, and wrap more properties.

### SOLID

Single Responsibility Principle

1. one module one role
2. separate data & logic

Open-Closed Principle = report display and printing should be 2 classes.

Liskov Substitution Principle = when using parent class, use child class.

Interface Segregation Principle (ISP)

1. separate data & logic
2. A rely on B, and B rely on C. A and B will be changed when changing C

Dependency Inversion Principle (DIP)

1. element-wise communications
2. rely on interface, not class. Classes changing a lot.


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