クラスのインスタンスをspreadしてもメソッドは複製されない

code:ts

class Greeter {

greeting: string;

constructor(message: string) {

this.greeting = message;

}

greet() {

return "Hello, " + this.greeting;

}

}

const x: Greeter = new Greeter("world");

const y: Greeter = { ...x };

// Property 'greet' is missing in type '{ greeting: string; }' but required in type 'Greeter'.