C# 实现 IEquatable.Equal

Question

我有这样一个类:

public class Foo<T> : IEquatable<T> where T : struct
{
    List<T> lst;
    [Other irrelevant member stuff]
}

我想实现 IEquatable<T> Foo 类的接口(interface)。我需要做什么。为简单起见，我只想检查列表成员是否相等。

谢谢。

C# 4.0 支持的答案是允许的。

更新:这是我目前拥有的:

public bool Equals(Foo<T> foo)
{
    return lst.Equals(foo.lst);
}

public override bool Equals(Object obj)
{
    if (obj == null) return base.Equals(obj);

    if (!(obj is Foo<T>))
    {
        throw new Exception("The 'obj' argument is not a Foo<T> object.");
    }
    else
    {
            return Equals(obj as Foo<T>)
    }
}    

public override int GetHashCode()
{
    return this.lst.GetHashCode();
}

public static bool operator ==(Foo<T> f1, Foo<T> f2)
{
   return f1.Equals(f2);
}

public static bool operator !=(Foo<T> f1, Foo<T> f2)
{
   return (!f1.Equals(f2));
}

我收到这个错误:

Error 1 'Foo<T>' does not implement interface member 'System.IEquatable<T>.Equals(T)

Answer 1

不幸的是，List<T>不会覆盖 Equals或 GetHashCode .这意味着即使您已经更正了类声明，您仍需要自己执行比较:

public bool Equals(Foo<T> foo)
{
    // These need to be calls to ReferenceEquals if you are overloading ==
    if (foo == null)
    {
        return false;
    }
    if (foo == this)
    {
        return true;
    }
    // I'll assume the lists can never be null
    if (lst.Count != foo.lst.Count)
    {
        return false;
    }
    for (int i = 0; i < lst.Count; i++)
    {
        if (!lst[i].Equals(foo.lst[i]))
        {
            return false;
        }
    }
    return true;
}

public override int GetHashCode()
{
    int hash = 17;
    foreach (T item in lst)
    {
        hash = hash * 31 + item.GetHashCode();
    }
    return hash;
}

public override bool Equals(Object obj)
{
    // Note that Equals *shouldn't* throw an exception when compared
    // with an object of the wrong type
    return Equals(obj as Foo<T>);
}

在重载 == 和 != 之前，我个人会非常仔细地考虑。如果您确实决定实现它们，您应该考虑其中一个或两个值都为 null 的情况:

public static bool operator ==(Foo<T> f1, Foo<T> f2)
{
   if (object.ReferenceEquals(f1, f2))
   {
       return true;
   }
   if (object.ReferenceEquals(f1, null)) // f2=null is covered by Equals
   {
       return false;
   }
   return f1.Equals(f2);
}