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typescript - 通过组合接口来创建一个带有区分字段的类型？

问题描述

通过组合接口来创建一个带有区分字段的类型？

这是我的代码：

/*
 * Missing changeFn indicates delete
 */
type IChangeRequestPromiseProxy<TEntity extends IBaseEntity> =
    | IUpdateRequestPromiseProxy<TEntity>
    | IDeleteRequestPromiseProxy;

interface IUpdateRequestPromiseProxy<TEntity extends IBaseEntity> {
    id: Id;
    resolve(value: IPersistence<TEntity>): void;
    reject(reason: any): void;
    changeFn(entity: TEntity): IPersistence<TEntity>;
}

interface IDeleteRequestPromiseProxy {
    id: Id;
    resolve(value: void): void;
    reject(reason: any): void;
    changeFn(entity: never): never;
}

let promiseProxy: IChangeRequestPromiseProxy<TEntity> = { id, resolve, reject };

这是我得到的错误。要点似乎是Property 'changeFn' is missing in type：

让 promiseProxy: IChangeRequestPromiseProxy Type '{ id: string; 解决：（值？：IPersistence | PromiseLike> | undefined）=> void；拒绝：（原因？：任何）=> 无效；}' 不可分配给类型 'IChangeRequestPromiseProxy'。'{ id: string; 类型中缺少属性 'changeFn' 解决：（值？：IPersistence | PromiseLike> | undefined）=> void；拒绝：（原因？：任何）=> 无效；}' 但在 'IUpdateRequestPromiseProxy'.ts(2322) Queue.service.ts(16, 5) 类型中是必需的：此处声明了 'changeFn'。

为什么这不起作用？

标签： typescript

解决方案

changeFn(entity: never): never;不会使该属性成为changeFn可选的。要使其成为可选，您可以使用声明它，?并且由于您实际上不需要任何值，因此它应该是类型undefined

从您的问题中添加缺少的类型，它看起来像：

type IChangeRequestPromiseProxy<TEntity extends IBaseEntity> =
    | IUpdateRequestPromiseProxy<TEntity>
    | IDeleteRequestPromiseProxy;

interface IUpdateRequestPromiseProxy<TEntity extends IBaseEntity> {
    id: Id;
    resolve(value: IPersistence<TEntity>): void;
    reject(reason: any): void;
    changeFn(entity: TEntity): IPersistence<TEntity>;
}

interface IDeleteRequestPromiseProxy {
    id: Id;
    resolve(value: void): void;
    reject(reason: any): void;
    changeFn?:undefined;
}

interface IBaseEntity {}
class Entity { }
interface IPersistence<T> { o: T}
type Id = string;
declare const id: string;
declare const resolve: (value: void) =>  void;
declare const reject: (value: any) =>  void;

let promiseProxy: IChangeRequestPromiseProxy<Entity> = { id, resolve, reject };

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