TypeScript 中的接口除了可用于对类的一部分行为进行抽象以外，也常用于对对象的形状（Shape）进行描述

    1. interface Shape {
    2.     head: string;
    3.     arm: string;
    4. }
    5. interface Person {
    6.     name: string;
    7.     age: number;
    8.     shape: Shape;
    9.     say(word: string): void;
    10. }
    11. let jack: Person = {
    12.     name: 'Jack',
    13.     age: 18,
    14.     shape: {
    15.         head: 'head',
    16.         arm: 'arm'
    17.     },
    18.     say(word: string) {
    19.         console.log(word)
    20.     }
    21. }
    22. jack.say('hi')

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