c# – 为什么接口类型的列表不能接受继承接口的意图？

public interface IPrimary{ void doBattle(); }

// an ISecondary "is" an IPrimary
public interface ISecondary : IPrimary {  }

// An implementation of ISecondary is also an IPrimary:
internal class SecondaryImpl : ISecondary
{
    // Required,since this is an IPrimary
    public void doBattle(){ }
}

为什么我不能这样做？

List<IPrimary> list = new List<ISecondary>();

这导致以下编译错误：

Argument type ‘System.Collections.Generic.List’ is not assignable to parameter type ‘System.Collections.Generic.List’

我明白错误,我意识到有解决方法.我只是看不到任何明确的原因,直接转换是不允许的.包含在ISecondary列表中的值应该完全是IPrimary类型的(扩展)值.然后列表< IPrimary>列表< ISecondary>被解释为不相关的类型？

任何人都可以清楚地解释C#设计的原因吗？

一个稍微扩展的例子：我试图做类似以下事情时遇到这个问题：

internal class Program
{
    private static void Main(string[] args)
    {
        // Instance of ISecondary,and by extention,IPrimary:
        var mySecondaryInstance = new SecondaryImpl();

        // This works as expected:
        AcceptImpl(mySecondaryInstance);

        // List of instances of ISecondary,which are also,// by extention,instances of IPrimary:
        var myListOfSecondaries = new List<ISecondary> {mySecondaryInstance};

        // This,however,does not work (results in a compilation error):
        AcceptList(myListOfSecondaries);
    }

    // Note: IPrimary parameter:
    public static void AcceptImpl(IPrimary instance){  }

    // Note: List of type IPrimary:
    public static void AcceptList(List<IPrimary> list){  }

}