C#SortedSet和相等

我对SortedSet的行为有些疑惑,请看下面的例子：

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());
}

如果Compare(x,y)返回0,则SortedSet将丢弃条目.可以防止这种情况,因为如果Equals()返回true,则SortedSet的行为类似于HashSet,并丢弃条目.

解决方法

如果在值相等并且Compare方法返回0时提供备用比较,则可以执行此操作.在大多数情况下,这可能只是推迟问题而不是解决问题.正如其他人所指出的那样,SortedSet丢弃了重复项,当您提供自定义比较器时,它使用它来确定重复性.

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