问题描述
为什么这不起作用?
public class ClassOptions {}
public interface Inode {
ClassOptions Options {get;}
}
public class MyClass : Inode {
public ClassOptions Options { get; set; }
}
public class ClassDerivedOptions : ClassOptions {
}
public class MyDerivedClass : Inode {
public ClassDerivedOptions Options { get; set; } << does not implement INode...
}
[ 编译器消息告诉我为什么它会中断，但我想知道编译器为什么不让它通过的原因 - 如果有任何解决方法?- 谢谢]
[ the compiler message tells me why it breaks but i'd like to know the reasoning behind why the compiler doesnt let this through - also if there are any work arounds? - thanks]
推荐答案
它不起作用，因为 INode 接口显式调用 ClassOptions 类型的 Options 属性.C# 不支持返回类型协方差(这是您在本例中所要求的).
It doesn't work because the INode interface explicitly calls for an Options property of type ClassOptions. C# doesn't support return type covariance (which is what you're asking for in this case).
对于它的价值，Microsoft Connect 上还有一个专门针对返回类型协方差的语言功能请求:
For what it's worth, there's also a language feature request on Microsoft Connect specifically for return type covariance:
需要 C#/所有 .NET 语言中的协变返回类型
如果您查看该页面，他们还提到常见的解决方法是使用显式接口实现:
If you look at the page, they also mention that the common work-around is to use Explicit Interface Implementation:
public class MyDerivedClass : INode
{
public ClassDerivedOptions Options { get; set; }
public ClassOptions INode.Options { get { return Options; } }
}
这篇关于由接口指定的属性的多态性的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持编程学习网！