实现相等运算符的抽象类
假设我定义了以下抽象类：
public abstract class ValueEquality<T> : IEquatable<T>
where T : ValueEquality<T>
{
public override bool Equals(object obj)
{
return Equals(obj as T);
}
public static bool operator ==(ValueEquality<T> lhs, object rhs)
{
if (ReferenceEquals(lhs, rhs))
{
return true;
}
else if (ReferenceEquals(lhs, null) || ReferenceEquals(rhs, null))
{
return false;
}
else
{
return lhs.Equals(rhs);
}
}
public static bool operator !=(ValueEquality<T> lhs, object rhs)
{
return !(lhs == rhs);
}
public bool Equals(T other)
{
return other != null && EqualNoNull(other);
}
public abstract override int GetHashCode();
public abstract bool EqualNoNull(T other);
}
然后创建一个类C，如下所示：
public class C : MyEquatable<C>
{
public override bool EqualsNoNull(C other)
{
...
}
public override int GetHashCode()
{
...
}
}
如果我有代码：
C x1;
C x2;
bool equal = x1 == x2;
这最终会调用 equals 方法C吗？这种方法有什么问题吗？
编辑：修复了答案引发的代码中的一些问题。
守着一只汪2回答
-
繁花如伊
此代码将执行无限循环：public override bool Equals(object obj){ try { T otherT = (T) obj; return Equals(this, otherT); } catch (InvalidCastException) { return false; }}它会Equals(object obj)一次又一次地调用。正确的实现：public abstract class MyEquatable<T> : IEquatable<T> where T : MyEquatable<T>{ 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 this.Equals((MyEquatable<T>)obj); } protected bool Equals(MyEquatable<T> other) { return this.Equals(other as T); } public static bool operator ==(MyEquatable<T> lhs, object rhs) { return Equals(lhs, rhs); } public static bool operator !=(MyEquatable<T> lhs, object rhs) { return Equals(lhs, rhs); } public abstract bool Equals(T other); public abstract override int GetHashCode();}x1 == x2将调用运算符==of MyEquatable，那将调用Equals(object obj)。最后，它在类中调用Equals(T other)覆盖C -
慕容3067478
遵循文档中通常建议的另一种实现public abstract class MyEquatable<T> : IEquatable<T> where T : MyEquatable<T> { public override bool Equals(object obj) { if (ReferenceEquals(obj, null) || obj.GetType() != GetType()) return false; var valueObject = obj as T; //Note the cast if (ReferenceEquals(valueObject, null)) return false; return Equals(valueObject); //Calls Equals(T other) } public abstract bool Equals(T other); public abstract override int GetHashCode(); public static bool operator ==(MyEquatable<T> left, MyEquatable<T> right) { if (ReferenceEquals(left, null) && ReferenceEquals(right, null)) return true; if (ReferenceEquals(left, null) || ReferenceEquals(right, null)) return false; return left.Equals(right); } public static bool operator !=(MyEquatable<T> left, MyEquatable<T> right) { return !(left == right); }}
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相关分类
C#