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创建可比较的字典键

dictionary collections vb.net c#

vulkanino · 技术社区 · 15 年前

我想使用字典(键,值),键不是基类型,而是一个类,如:

Public Class MyKey

    Sub New(ByVal packet As String, ByVal sent As Boolean)
        Me.packet = packet.ToUpper.Trim
        Me.sent = sent
    End Sub

    Private packet As String
    Private sent As Boolean
End Class

Public Class MyKey
    Implements System.IEquatable(Of MyKey)


    Sub New(ByVal packet As String, ByVal sent As Boolean)
        Me.packet = packet.ToUpper.Trim
        Me.sent = sent
    End Sub

    Public Overloads Function Equals(ByVal other As MyKey) As Boolean Implements IEquatable(Of MyKey).Equals
        Return other.sent = Me.sent AndAlso other.packet = Me.packet
    End Function


    Private packet As String
    Private sent As Boolean
End Class

但要取得一致的结果,我还必须实施对象。等于以及Object.GetHashCode:

Public Class MyKey
    Implements System.IEquatable(Of MyKey)


    Sub New(ByVal packet As String, ByVal sent As Boolean)
        Me.packet = packet.ToUpper.Trim
        Me.sent = sent
    End Sub

    Public Overloads Function Equals(ByVal other As ChiavePietanza) As Boolean Implements IEquatable(Of MyKey).Equals
        Return other.sent = Me.sent AndAlso other.packet = Me.packet
    End Function

    Overrides Function Equals(ByVal o As Object) As Boolean
        Dim cast As MyKey = DirectCast(o, MyKey)
        Return Equals(cast)
    End Function

    Public Overrides Function GetHashCode() As Integer
        Return packet.GetHashCode Or sent.GetHashCode
    End Function


    Private packet As String
    Private sent As Boolean
End Class

问题是:GetHashCode实现正确吗?我应该如何实现它,返回一个将字符串和布尔哈希码合并的哈希码?

4 回复 | 直到 15 年前

JaredPar 15 年前

GetHashCode函数是正确的,并且符合哈希代码实现的已知规则。特别地

MyKey
美奇钥匙

packet 和 sent 是 ReadOnly 领域。现在暗示他们是 只读 因为它们在GetHashCode函数中使用。然而,未来的开发人员可能会忽略这一点,改变值并破坏GetHashCode所需的契约。明确地拥有它们 只读

另一个小音符。虽然这是个好主意 IEquatable(Of T) Dictionary Equals GetHashCode 方法,以便在 字典

Hans Passant 15 年前

它是okayish,但是Or操作符不能生成分布良好的散列值,因为它只能打开位,而不能关闭位。改用Xor运算符。

Community Mohan Dere 9 年前

GetHashCode 覆盖来自:

SO - What is the best algorithm for an overridden System.Object.GetHashCode? 所以你可以这样做:

public override int GetHashCode() {
    int hash = 17;
    hash = (hash * 23) + ((packet != null) ? packet.GetHashCode() : 0);
    hash = (hash * 23) + ((sent != null) ? sent.GetHashCode() : 0);
    return hash;
}

它应该直接移植到VB。

supercat 15 年前