sampleDocument 不可分配给类型 T

Question

我是 TypeScript 的新手，正在尝试使用它来掌握 OOP。

我有以下代码：

import {ReadOnlyDocument} from "../../docs/read-only.document";
import {IReadOnlyRepository} from "./abstract/Iread-only.repository";
import {sampleDocument} from "../../docs/sampleDocument";

export abstract class ReadOnlyRepository<T extends ReadOnlyDocument> implements IReadOnlyRepository<T> {

    public getById(id: string): T {
        let sample: sampleDocument = new sampleDocument('',
            new Date(),
            '',
            new Date(),
            '');
        /*Line of code that brings the error.*/
        return sample;
    }

}

但是我不断收到错误 sampleDocument is not assignable to type T，我似乎无法弄清楚出了什么问题。任何帮助将不胜感激。

我在下面添加了其他可能相关的代码。

import {ReadOnlyDocument} from "./read-only.document";

export class sampleDocument extends ReadOnlyDocument{

}

export abstract class Document {
    constructor(
        public id: string,
        public createdDate: Date,
        public createdBy: string,
        public updatedDate: Date,
        public updatedBy: string
    ) { }
}

import { Document } from './abs/document'

export abstract class ReadOnlyDocument extends Document{

}

import {ReadOnlyDocument} from "../../../docs/read-only.document";
import { IRepository } from "./Irepository";

export interface IReadOnlyRepository<T extends ReadOnlyDocument> extends IRepository<T> {
    getById(id: string): T;
}

import {Document} from "../../../domain/documents/abstract/document";

export interface IRepository<T extends Document>  {

}

Answer 1

T 是ReadOnlyDocument 的任何子类型，例如如果你有一个ReadOnlyPDF 并且扩展了ReadOnlyDocument，那么你可以构造一个ReadOnlyRepository<ReadOnlyPDF>，并且你希望它从getById 返回一个ReadOnlyPDF，但是它只返回一个ReadOnlyDocument。