类型兼容性
最后更新于：2022-04-02 03:28:14
[TOC]
## 概述
`Person`没有明确说明是基于`Named`的,但是有也不错报错
```
interface Named {
name: string;
}
class Person {
name: string;
}
let p: Named;
// OK, because of structural typing
p = new Person();
```
## 符合接口的赋值
只要变量符合接口的属性即可,额外属性不会报错
```
interface Named {
name: string;
}
let x: Named;
// y's inferred type is { name: string; location: string; }
let y = { name: 'Alice', location: 'Seattle' };
x = y;
```
## 比较两个函数
额外参数在 js 中非常常见
```
let x = (a: number) => 0;
let y = (b: number, s: string) => 0;
y = x; // OK
x = y; // Error
```
返回值比较
```
let x = () => ({name: 'Alice'});
let y = () => ({name: 'Alice', location: 'Seattle'});
x = y; // OK
y = x; // Error, because x() lacks a location property
```
## 函数重载
### 枚举
枚举类型与数字类型兼容，并且数字类型与枚举类型兼容。不同枚举类型之间是不兼容的
```
enum Status { Ready, Waiting };
enum Color { Red, Blue, Green };
let status = Status.Ready;
status = Color.Green; // Error
```
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