C＃的SortedSet< T>和平等 [英] C# SortedSet<T> and equality

问题描述

我有点纳闷有关的SortedSet的行为，见下面的例子：

I am a bit puzzled about the behaviour of SortedSet, see following example:

public class Blah
{
    public double Value { get; private set; }

    public Blah(double value)
    {
        Value = value;
    }
}

public class BlahComparer : Comparer<Blah>
{
    public override int Compare(Blah x, Blah y)
    {
        return Comparer<double>.Default.Compare(x.Value, y.Value);
    }
}

public static void main()
{
    var blahs = new List<Blah> {new Blah(1), new Blah(2), 
                                new Blah(3), new Blah(2)}

    //contains all 4 entries
    var set = new HashSet<Blah>(blahs); 

    //contains only Blah(1), Blah(2), Blah(3)
    var sortedset = new SortedSet<Blah>(blahs, new BlahComparer());
}

所以，如果比较的SortedSet丢弃条目（X，Y）返回0。我可以避免这种情况，这样，我的SortedSet的行为像HashSet的，并丢弃条目仅等于（）返回true？

So SortedSet discards entries if Compare(x,y) returns 0. Can I prevent this, such that my SortedSet behaves like HashSet and discards entries only if Equals() returns true?

推荐答案

您可以这样做如果您提供当值相等和比较的方法将否则返回0。在大多数情况下，这可能只是推迟问题，而不是解决它的另一种比较。正如其他人所指出的那样，SortedSet的丢弃重复，当你提供一个自定义比较它使用它来确定口是心非。

You can do this if you provide an alternate comparison when the Values are equal and the Compare method would otherwise return 0. In most cases this would probably just defer the problem instead of solving it. As others have noted, the SortedSet discards duplicates and when you provide a custom comparer it uses that to determine duplicity.

    static void Main(string[] args)
    {
        var blahs = new List<Blah>
                        {
                            new Blah(1, 0), new Blah(2, 1),
                            new Blah(3, 2), new Blah(2, 3)
                        };

        blahs.Add(blahs[0]);

        //contains all 4 entries
        var set = new HashSet<Blah>(blahs);

        //contains all 4 entries
        var sortedset = new SortedSet<Blah>(blahs, new BlahComparer());

    }
}

public class Blah
{
    public double Value { get; private set; }

    public Blah(double value, int index)
    {
        Value = value;
        Index = index;
    }

    public int Index { get; private set; }

    public override string ToString()
    {
        return Value.ToString();
    }
}

public class BlahComparer : Comparer<Blah>
{
    public override int Compare(Blah x, Blah y)
    {
        // needs null checks
        var referenceEquals = ReferenceEquals(x, y);
        if (referenceEquals)
        {
            return 0;
        }
        var compare = Comparer<double>.Default.Compare(x.Value, y.Value);
        if (compare == 0)
        {
            compare = Comparer<int>.Default.Compare(x.Index, y.Index);
        }
        return compare;
    }
}

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