面向对象的投放错误

问题描述

将派生类铸造为基类

我有一个通用的基本抽象类，它继承自IComparable，其定义如下

I have a base abstract class which is generic and inherits from IComparable which is defined like below

public abstract class BaseClass<T> where T : IComparable
{
    protected readonly T Data;

    protected BaseClass(T data)
    {
        Data = data;
    }

    public abstract T Get();

}

然后，我定义了一个类，该类继承自该基类并具有特定的泛型类型，其定义如下:

Then I have defined a classe which inherits from this base class and has a specific generic type and is defined like below:

public class Name : BaseClass<String>
{
    public Name(string data) : base(data)
    {
    }

    public override string Get()
    {
        throw new NotImplementedException();
    }
}

由于泛型是字符串，并且字符串是从IComparable继承的，所以我希望能够将具有字符串值的新Name对象定义为泛型，但是这样定义Name对象时会出现强制转换错误:

As generic type is string and string inherits from IComparable, I expect to be able to define new Name object with string value as generic type, but I get casting error for defining Name object like this:

BaseClass<IComparable> obj;
obj = new Name("behro0z");

，错误是

推荐答案

您要声明类型为BaseClass<T>的变量，并将T替换为IComparable.

You're declaring a variable of type BaseClass<T>, and substitute T with IComparable.

那是有效的，但这不是您的Name类的 .即使string实现了IComparable，该内容还是来自BaseClass<string>，不是 BaseClass<IComparable>.

That's valid, but that's not what your Name class is. That one derives from BaseClass<string>, not BaseClass<IComparable>, even though string implements IComparable.

您可以将变量obj声明为BaseClass<string>类型，或者将其派生为其他类型Name.

You can either declare your variable obj to be of type BaseClass<string>, or the more derived type, Name.

阅读协方差， C#泛型继承问题.

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