Question

我正在尝试将Definition类型的两个哈希集比较为EqualityComparer<T>.Default.Equals(value, oldValue)。 Definition定义如下

public class Definition
{
    public string Variable { get; set; }
    public HashSet<Location> LocationList { get; set; }

    public override bool Equals(object obj)
    {
        Definition other = obj as Definition;
        return other.Variable.Equals(this.Variable) && other.LocationList!= null &&this.LocationList != null
            && other.LocationList.Count == this.LocationList.Count
            && other.LocationList == this.LocationList;
    }

    public override int GetHashCode()
    {
        return this.Variable.GetHashCode() ^ this.LocationList.Count.GetHashCode();// ^ this.LocationList.GetHashCode();
    }
}

public class Location
{
    public int Line { get; set; }
    public int Column { get; set; }
    public int Position { get; set; }
    public string CodeTab { get; set; }
    public Location(int line, int col, int pos, string tab)
    {
        Line = line;
        Column = col;
        Position = pos;
        CodeTab = tab;
    }
    public override bool Equals(object obj)
    {
        Location other = obj as Location;
        return this.CodeTab == other.CodeTab
            && this.Position == other.Position
            && this.Column == other.Column
            && this.Line == other.Line;
    }
    public override int GetHashCode()
    {
        return this.CodeTab.GetHashCode() ^ this.Position.GetHashCode() 
            ^ this.Column.GetHashCode() ^ this.Line.GetHashCode();
    }
}

对于类似的集合，尽管所有信息保持不变，但结果仍返回为false。唯一的区别是某些元素的位置是互换的，但我知道HashSet在比较时不会保留或检查顺序。任何人都可以告诉我这里出了什么问题吗？

PS：我也尝试取消注释this.LocationList.GetHashCode()，但没有效果。

Answer 1

EqualityComparer<T>.Default将查找实现IEquatable<T>的对象。否则，它将推迟到ObjectEqualityComparer，它只检查引用相等性。这就是比较引用时看到错误的原因。

您真正想要做的是明确实施IEquatable<Location>。请注意，您应该确保您的属性不可变，以使其正常工作：

public class Location : IEquatable<Location>
{       
    public Location(int line, int col, int pos, string tab)
    {
        Line = line;
        Column = col;
        Position = pos;
        CodeTab = tab;
    }

    public int Line { get; private set; }
    public int Column { get; private set; }
    public int Position { get; private set; }
    public string CodeTab { get; private set; }

    public bool Equals(Location other)
    {
        if (ReferenceEquals(null, other)) return false;
        if (ReferenceEquals(this, other)) return true;
        return string.Equals(CodeTab, other.CodeTab) && Column == other.Column && Line == other.Line && Position == other.Position;
    }

    public override bool Equals(object obj)
    {
        if (ReferenceEquals(null, obj)) return false;
        if (ReferenceEquals(this, obj)) return true;
        if (obj.GetType() != this.GetType()) return false;
        return Equals((Location) obj);
    }

    public static bool operator ==(Location left, Location right)
    {
        return Equals(left, right);
    }

    public static bool operator !=(Location left, Location right)
    {
        return !Equals(left, right);
    }

    public override int GetHashCode()
    {
        unchecked
        {
            var hashCode = (CodeTab != null ? CodeTab.GetHashCode() : 0);
            hashCode = (hashCode*397) ^ Column;
            hashCode = (hashCode*397) ^ Line;
            hashCode = (hashCode*397) ^ Position;
            return hashCode;
        }
    }
}

现在，如果您查看EqualityComparer创建的Default类型，您会看到GenericEqualityComparer<Location>：

Console.WriteLine(EqualityComparer<Location>.Default.GetType())

Answer 2

您需要为集合创建比较器：

-fdelayed-branch

检查与对象的HashSet的相等性

2 个答案: