C#中值相等的自定义类的最强大的Equals实现

发布时间：2020-12-16 01:29:56 所属栏目：百科来源：网络整理

导读：假设我有一个Point2类,我想实现以下Equals： public override bool Equals ( object obj )public bool Equals ( Point2 obj ) 这来自Effective C#3书： public override bool Equals ( object obj ){ // STEP 1: Check for null if ( obj == null ) { return

假设我有一个Point2类,我想实现以下Equals：

public override bool Equals ( object obj )

public bool Equals ( Point2 obj )

这来自Effective C#3书：

public override bool Equals ( object obj )
{
    // STEP 1: Check for null
    if ( obj == null )
    {
        return false;
    }

    // STEP 3: equivalent data types
    if ( this.GetType ( ) != obj.GetType ( ) )
    {
        return false;
    }
    return Equals ( ( Point2 ) obj );
}

public bool Equals ( Point2 obj )
{
    // STEP 1: Check for null if nullable (e.g.,a reference type)
    if ( obj == null )
    {
        return false;
    }
    // STEP 2: Check for ReferenceEquals if this is a reference type
    if ( ReferenceEquals ( this,obj ) )
    {
        return true;
    }
    // STEP 4: Possibly check for equivalent hash codes
    if ( this.GetHashCode ( ) != obj.GetHashCode ( ) )
    {
        return false;
    }
    // STEP 5: Check base.Equals if base overrides Equals()
    System.Diagnostics.Debug.Assert (
        base.GetType ( ) != typeof ( object ) );

    if ( !base.Equals ( obj ) )
    {
        return false;
    }

    // STEP 6: Compare identifying fields for equality.
    return ( ( this.X.Equals ( obj.X ) ) && ( this.Y.Equals ( obj.Y ) ) );
}

这有点矫枉过正吗？

解决方法

支持与继承层次结构的相等性是棘手的.你需要弄清楚你的意思.你真的需要继承吗？如果不是 – 如果Point2直接从System.Object派生,并且你可以使它密封,生活变得容易一些.在那种情况下,我会使用：

public override bool Equals (object obj)
{
    return Equals(obj as Point2);
}

public bool Equals (Point2 obj)
{
    // STEP 1: Check for null if nullable (e.g.,a reference type)
    // Note use of ReferenceEquals in case you overload ==.
    if (object.ReferenceEquals(obj,null))
    {
        return false;
    }

    // STEP 2: Check for ReferenceEquals if this is a reference type
    // Skip this or not? With only two fields to check,it's probably
    // not worth it. If the later checks are costly,it could be.
    if (object.ReferenceEquals( this,obj))
    {
        return true;
    }

    // STEP 4: Possibly check for equivalent hash codes
    // Skipped in this case: would be *less* efficient

    // STEP 5: Check base.Equals if base overrides Equals()
    // Skipped in this case

    // STEP 6: Compare identifying fields for equality.
    // In this case I'm using == instead of Equals for brevity
    // - assuming X and Y are of a type which overloads ==.
    return this.X == obj.X && this.Y == obj.Y;
}

（编辑：李大同）

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