1

考虑这个类，它重载了 Person 类的 = 运算符。这适用于 VB.NET：

Public Class Person

    Public Sub New(ByVal FirstName As String, ByVal LastName As String)
        _FirstName = FirstName
        _LastName = LastName
    End Sub

    Private _LastName As String
    Public Property LastName() As String
        Get
            Return _LastName
        End Get
        Set(ByVal value As String)
            _LastName = value
        End Set
    End Property

    Private _FirstName As String
    Public Property FirstName() As String
        Get
            Return _FirstName
        End Get
        Set(ByVal value As String)
            _FirstName = value
        End Set
    End Property

    Public Shared Operator <>(ByVal Person1 As Person, ByVal Person2 As Person) As Boolean
        Return Not (Person1 = Person2)
    End Operator


    Public Shared Operator =(ByVal Person1 As Person, ByVal Person2 As Person) As Boolean
        Return Person1.FirstName = Person2.FirstName AndAlso Person1.LastName = Person2.LastName
    End Operator

    Public Class Test

        Public Sub TestIt()

            Dim P1 As New Person("f1", "l1")
            Dim P2 As Person = Nothing

            Dim IsEqual As Boolean = False

            If P1 IsNot Nothing AndAlso P2 IsNot Nothing Then

                If P1 = P2 Then
                    IsEqual = True
                End If

            End If

        End Sub
    End Class
End Class

和 C# 中的同一个类：

public Person(string FirstName, string LastName)
{
    _FirstName = FirstName;
    _LastName = LastName;
}

private string _LastName;
public string LastName
{
    get { return _LastName; }
    set { _LastName = value; }
}

private string _FirstName;
public string FirstName
{
    get { return _FirstName; }
    set { _FirstName = value; }
}

public static bool operator !=(Person Person1, Person Person2)
{
    return !(Person1 == Person2);
}


public static bool operator ==(Person Person1, Person Person2)
{
    return Person1.FirstName == Person2.FirstName && Person1.LastName == Person2.LastName;
}

public class Test
{
    public void TestIt()
    {
        Person P1 = new Person("f1", "l1");
        Person P2 = null;

        bool IsEqual = false;


        if (P1 != null && P2 != null)
        {
            if (P1 == P2)
            {
                IsEqual = true;
            }
        }
    }
}

使用 C# 类，如果在Person测试中使用null该==函数是否为null. 也就是说，是否有与测试Is Nothing分开的与VB 等效的对应功能==？似乎 C#==两者都使用。

我试过了object.IsEqual；那看起来也错了。

4

2 回答 2

3

顺便说一句，由于您正在实施，==您还应该覆盖 Equals（和 GetHashCode）。

一个简单的方法是实现IEquatable<Person>：

public bool Equals(Person other)
{
    return other != null &&
           FirstName == other.FirstName &&
           LastName == other.LastName;
}

然后覆盖 Equals：

public override bool Equals(object o)
{
    var other = o as Person;
    return other != null && this.Equals(other);
}

最后==只是：

public static bool operator ==(Person left, Person right)
{
    return object.Equals(left, right);
}

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

（object.Equals handsnull正确。）

于 2012-08-23T03:41:56.813 回答
1

检查null您的重载运算符也使用object.ReferenceEquals：

public static bool operator ==(Person Person1, Person Person2)
{
    if(object.ReferenceEquals(Person1, null)) {
        return object.ReferenceEquals(Person2, null);
    } else if(object.ReferenceEquals(Person2, null)) {
        return false;
    } else {
        return Person1.FirstName == Person2.FirstName && Person1.LastName == Person2.LastName;
    }
}

或者，更简洁地说：

return object.ReferenceEquals(person1, person2) || (
           !object.ReferenceEquals(person1, null)
        && !object.ReferenceEquals(person2, null)
        && person1.FirstName == person2.FirstName
        && person1.LastName  == person2.LastName);
于 2012-08-23T03:14:41.273 回答