c# - C# 子类中的 protected 属性是否应该隐藏对父类公共(public)属性的访问？

Question

我有以下代码:

public class Parent
{
    public string MyField { get; set; }
}

public class Child : Parent
{
    protected new int MyField { get; set; }
}

我尝试通过以下方式访问它:

static void Main(string[] args)
{
    Child child = new Child();
    child.MyField = "something";
}

Visual studio 2008 编译时没有注释，但在 Mono(2.4.2，Ubuntu)下我收到错误消息

'HideTest.Child.MyField' is inaccessible due to its protection level (CS0122)

是一种实现还是另一种更符合这里的标准？

编辑:感谢所有指出错误设计的人。不幸的是，它是一个第三方库，对其进行重大更改是不切实际的。

Answer 1

来自 ECMA-334 (C# 规范)§10.7.1.2:

A declaration of a new member hides an inherited member only within the scope of the new member.

您可以通过在 Microsoft 的实现上运行此测试来查看此行为。

using System;
using NUnit.Framework;

namespace ScratchPad
{
    [TestFixture]
    public class Class1
    {
        [Test]
        public void InheritanceHiding()
        {
            var b = new Base();
            var d = new Derived();

            var baseSomeProperty = b.SomeProperty;
            var derivedSomeProperty = d.SomeProperty;

            b.GetSomeProperty();
            d.GetSomeProperty();
        }
    }

    public class Base
    {
        public string SomeProperty
        {
            get
            {
                Console.WriteLine("Getting Base.SomeProperty");
                return "Base.SomeProperty";
            }
        }

        public string GetSomeProperty()
        {
            return SomeProperty;
        }
    }

    public class Derived : Base
    {
        protected new int SomeProperty
        {
            get
            {
                Console.WriteLine("Getting Derived.SomeProperty");
                return 3; //Determined by random roll of the dice.
            }
        }

        public new int GetSomeProperty()
        {
            return SomeProperty;
        }
    }
}

输出:

Getting Base.SomeProperty    //(No Controversy)  
Getting Base.SomeProperty    //(Because you're calling from public scope and the new member is in protected scope, there is no hiding)  
Getting Base.SomeProperty    //(No Controversy)  
Getting Derived.SomeProperty //(Now because you're calling from protected scope, you get the protected member).

因此，您从 Main() 访问的属性应该是基类属性(在 MS.NET 中)，而不是派生属性(在 Mono 中)，因为新派生成员仅在 protected 范围内隐藏“旧”基础成员。

根据规范，Mono 在这里做错了。