打字稿联合类型不起作用 [英] Typescript union type not working

问题描述

我有以下课程:

export interface ISimpleUser {
    id: number;
    full_name: string;
}


export interface IMember extends ng.resource.IResource<IMember> {
    id: number;
    project: number;
    user: number|ISimpleUser;
    skills: ISkill[];
    about: string;
    accepted: Boolean;

    updated: Date;
    created: Date;
}

在某些时候，我想遍历一组成员，如下例所示:

At some point I want to iterate over an arroy of members like in the following example:

        return angular.forEach<resources.IMember>(this.project.members,
            (member: resources.IMember) => {
                return member.user.id == user.id;
            }).length > 0;

但我收到此错误:

error TS2339: Property 'id' does not exist on type 'number | ISimpleUser'

不知道到底是哪里出了问题.我看到代码的其他部分使用联合类型.

Don't know what is wrong exactly. I see other parts of the code working with the union types.

谢谢.

推荐答案

你需要做一些类型检查和强制转换来处理这种情况:

You will need to do some type checking and casting to handle this scenario:

(member: resources.IMember) => {
  return member.user.id == user.id;
  if (typeof (member.user) === 'number') {
    return member.user == user.id;
  } else {
    return (<ISimpleUser>member.user).id == user.id;
  }
}).length > 0;

仅仅因为您在代码/设计时知道可能的类型并不意味着编译代码在运行时知道类型.因此，您可以检查 member.user 的类型以查看它是否为数字，然后有条件地进行比较.

Just because you know the possible types at code/design time does not mean that the compiles code knows types at run time. So you can check the type of member.user to see if it is a number then conditionally do your comparison.

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