用对象的 HashSet 检查相等性答案

【问题标题】：Checking equality with a HashSet of objects用对象的 HashSet 检查相等性
【发布时间】：2015-12-15 09:03:31
【问题描述】：

我正在尝试将Definition 类型的两个哈希集与EqualityComparer<T>.Default.Equals(value, oldValue) 进行比较。 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();
    }
}

不知何故，对于类似的集合，结果返回为false，尽管所有信息都保持不变。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。谁能告诉我这里出了什么问题？

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

【问题讨论】：

这是HashSet<Location> 不是HashSet<Definition>，但您声明要比较“定义的两个哈希集”。所以要么你的问题问错了，要么你的代码做了不同的事情。
value 和 oldValue 是 Definition 类型。

标签： c# hashset iequalitycomparer

【解决方案1】：

您需要为集合创建一个比较器：

var setComparer = HashSet<Location>.CreateSetComparer();
return other.Variable.Equals(this.Variable) && setComparer.Equals(this.LocationList, other.LocationList);

【讨论】：

【解决方案2】：

EqualityComparer<T>.Default 将寻找实现IEquatable<T> 的对象。否则，它将遵循ObjectEqualityComparer，它只是检查引用是否相等。这就是为什么您在比较引用时看到错误的原因。

您真正想要做的是显式实现IEquatable<Location>。请注意，您确实应该使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，如果您查看由Default 创建的类型EqualityComparer，您将看到GenericEqualityComparer<Location>：

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

【讨论】：