TS展开一个对象实例时，将会丢失其方法
示例：
class C {
p = 12;
m() {
}
}
let c = new C();
let clone = { ...c };
clone.p; // ok
clone.m(); // error!
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class C {
p = 12;
m() {
}
}
let c = new C();
let clone = { ...c };
clone.p; // ok
clone.m(); // error!