多态性通过接口指定的属性 [英] polymorphism for properties specified by interfaces

问题描述

为什么犯规这项工作？

Why doesnt this work?

 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...
}

[编译器的消息告诉我，为什么它打破但我想知道为什么后面编译犯规让这个通过推理 - 也是，如果有任何变通？ - 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的界面明确要求类型ClassOptions的选项属性。 C＃不支持返回类型的协方差（这是你在这种情况下，要求的东西）。

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).

有关它的价值，但也对微软的语言功能要求专为连接返回类型的协方差：

For what it's worth, there's also a language feature request on Microsoft Connect specifically for return type covariance:

的在C＃中需要协变返回类型/所有.NET语言

如果你看网页，他们还提到了共同的解决办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; } }
}

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