如何在一个参数中编写具有固定类型的多态函数

// 定义一个接口，描述需要实现的方法
interface Printable {
    print(): void;
}

// 实现接口的具体类
class Document implements Printable {
    content: string;

    constructor(content: string) {
        this.content = content;
    }

    print() {
        console.log(`Printing document: ${this.content}`);
    }
}

class Photo implements Printable {
    url: string;

    constructor(url: string) {
        this.url = url;
    }

    print() {
        console.log(`Printing photo from URL: ${this.url}`);
    }
}

// 泛型函数，接受实现了Printable接口的任何类型
function printItem<T extends Printable>(item: T): void {
    item.print();
}

// 使用示例
const doc = new Document("Sample Document");
const photo = new Photo("https://example.com/photo.jpg");

printItem(doc);  // 输出: Printing document: Sample Document
printItem(photo); // 输出: Printing photo from URL: https://example.com/photo.jpg