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;
}
}
