是否不强制执行联合类型？

Question

这不应该失败吗？

class Animal { }
class Person { }

type MyUnion = Number | Person;

var list: Array<MyUnion> = [ "aaa", 2, new Animal() ]; // Shouldn't this fail?

var x: MyUnion = "jjj"; // Shouldn't this fail?

在这种情况下有没有办法强制执行类型检查？

Answer 1

如果 Animal 或 Person 定义任何内容，它将失败:

class Animal { name: string; }
class Person { age: Number; }

type MyUnion = Number | Person;

var list: Array<MyUnion> = [ "aaa", 2, new Animal() ]; // Fails now

var x: MyUnion = "jjj"; // Fails now

由于您没有在 Animal 或 Person 中定义任何内容，因此字符串（或任何其他内容）满足您要求的合同。

Answer 2

TypeScript 根据 structural subtyping.

处理类型兼容性

Structural typing is a way of relating types based solely on their members

特别是 类:

When comparing two objects of a class type, only members of the instance are compared. Static members and constructors do not affect compatibility.

更多信息请访问 https://www.typescriptlang.org/docs/handbook/type-compatibility.html#classes