IEqualityComparer<T> インターフェイス


オブジェクトの等価比較をサポートするメソッドを定義します。Defines methods to support the comparison of objects for equality.

generic <typename T>
public interface class IEqualityComparer
public interface IEqualityComparer<in T>
type IEqualityComparer<'T> = interface
Public Interface IEqualityComparer(Of In T)



比較するオブジェクトの型。The type of objects to compare.


次の例では、カスタム Box オブジェクトをディクショナリコレクションに追加します。The following example adds custom Box objects to a dictionary collection. ディメンションが同じである場合、Box オブジェクトは等しいと見なされます。The Box objects are considered equal if their dimensions are the same.

using System;
using System.Collections.Generic;

class Example
   static void Main()
      BoxEqualityComparer boxEqC = new BoxEqualityComparer();

      var boxes = new Dictionary<Box, string>(boxEqC);

      var redBox = new Box(4, 3, 4);
      AddBox(boxes, redBox, "red");
      var blueBox = new Box(4, 3, 4);
      AddBox(boxes, blueBox, "blue");
      var greenBox = new Box(3, 4, 3);
      AddBox(boxes, greenBox, "green");
      Console.WriteLine("The dictionary contains {0} Box objects.",

   private static void AddBox(Dictionary<Box, String> dict, Box box, String name)
      try {
         dict.Add(box, name);
      catch (ArgumentException e) {
         Console.WriteLine("Unable to add {0}: {1}", box, e.Message);

public class Box
    public Box(int h,  int l, int w)
        this.Height = h;
        this.Length = l;
        this.Width = w;

    public int Height { get; set; }
    public int Length { get; set; }
    public int Width { get; set; }

    public override String ToString()
       return String.Format("({0}, {1}, {2})", Height, Length, Width);

class BoxEqualityComparer : IEqualityComparer<Box>
    public bool Equals(Box b1, Box b2)
        if (b2 == null && b1 == null)
           return true;
        else if (b1 == null || b2 == null)
           return false;
        else if(b1.Height == b2.Height && b1.Length == b2.Length
                            && b1.Width == b2.Width)
            return true;
            return false;

    public int GetHashCode(Box bx)
        int hCode = bx.Height ^ bx.Length ^ bx.Width;
        return hCode.GetHashCode();
// The example displays the following output:
//    Unable to add (4, 3, 4): An item with the same key has already been added.
//    The dictionary contains 2 Box objects.
Imports System.Collections.Generic

Module Example
   Public Sub Main()

      Dim boxEqC As New BoxEqualityComparer()

      Dim boxes As New Dictionary(Of Box, String)(boxEqC)

      Dim redBox = New Box(4, 3, 4)
      AddBox(boxes, redBox, "red")

      Dim blueBox = new Box(4, 3, 4)
      AddBox(boxes, blueBox, "blue")

      Dim greenBox = new Box(3, 4, 3)
      AddBox(boxes, greenBox, "green")

      Console.WriteLine("The dictionary contains {0} Box objects.",
   End Sub

   Private Sub AddBox(dict As Dictionary(Of Box, String), box As Box, name As String)
         dict.Add(box, name)
      Catch e As ArgumentException
         Console.WriteLine("Unable to add {0}: {1}", box, e.Message)
      End Try
   End Sub
End Module

Public Class Box
    Private _Height As Integer
    Private _Length As Integer
    Private _Width As Integer

    Public Sub New(ByVal h As Integer, ByVal l As Integer,
                                        ByVal w As Integer)
        Me.Height = h
        Me.Length = l
        Me.Width = w
    End Sub

    Public Property Height() As Integer
            Return _Height
        End Get
        Set(ByVal value As Integer)
            _Height = value
        End Set
    End Property

    Public Property Length() As Integer
            Return _Length
        End Get
        Set(ByVal value As Integer)
            _Length = value
        End Set
    End Property

    Public Property Width() As Integer
            Return _Width
        End Get
        Set(ByVal value As Integer)
            _Width = value
        End Set
    End Property

    Public Overrides Function ToString() As String
       Return String.Format("({0}, {1}, {2})", _Height, _Length, _Width)
    End Function
End Class

Class BoxEqualityComparer
    Implements IEqualityComparer(Of Box)

    Public Overloads Function Equals(ByVal b1 As Box, ByVal b2 As Box) _
                   As Boolean Implements IEqualityComparer(Of Box).Equals

        If b1 Is Nothing AndAlso b2 Is Nothing Then
            Return True
        ElseIf b1 Is Nothing Or b2 Is Nothing Then
            Return False
        ElseIf b1.Height = b2.Height AndAlso b1.Length =
                b2.Length AndAlso b1.Width = b2.Width Then
            Return True
            Return False
        End If
    End Function

    Public Overloads Function GetHashCode(ByVal bx As Box) _
                As Integer Implements IEqualityComparer(Of Box).GetHashCode
        Dim hCode As Integer = bx.Height Xor bx.Length Xor bx.Width
        Return hCode.GetHashCode()
    End Function

End Class
' The example displays the following output:
'    Unable to add (4, 3, 4): An item with the same key has already been added.
'    The dictionary contains 2 Box objects.


このインターフェイスを使用すると、コレクションに対してカスタマイズされた等値比較を実装できます。This interface allows the implementation of customized equality comparison for collections. つまり、T型に対して独自の等価定義を作成し、この定義を IEqualityComparer<T> ジェネリックインターフェイスを受け入れるコレクション型と共に使用するように指定できます。That is, you can create your own definition of equality for type T, and specify that this definition be used with a collection type that accepts the IEqualityComparer<T> generic interface. .NET Framework では、Dictionary<TKey,TValue> ジェネリックコレクション型のコンストラクターがこのインターフェイスを受け入れます。In the .NET Framework, constructors of the Dictionary<TKey,TValue> generic collection type accept this interface.

このインターフェイスの既定の実装は、EqualityComparer<T> ジェネリッククラスの Default プロパティによって提供されます。A default implementation of this interface is provided by the Default property of the EqualityComparer<T> generic class. StringComparer クラスは String型の IEqualityComparer<T> を実装します。The StringComparer class implements IEqualityComparer<T> of type String.

このインターフェイスでは、等価比較のみがサポートされます。This interface supports only equality comparisons. 並べ替えと順序付けの比較のカスタマイズは、IComparer<T> ジェネリックインターフェイスによって提供されます。Customization of comparisons for sorting and ordering is provided by the IComparer<T> generic interface.

EqualityComparer<T> クラスは、Object.Equals メソッドではなく IEquatable<T>.Equals メソッドを使用して等しいかどうかをテストするため、IEqualityComparer<T> インターフェイスを実装するのではなく、EqualityComparer<T> クラスから派生させることをお勧めします。We recommend that you derive from the EqualityComparer<T> class instead of implementing the IEqualityComparer<T> interface, because the EqualityComparer<T> class tests for equality using the IEquatable<T>.Equals method instead of the Object.Equals method. これは、Dictionary<TKey,TValue> クラスおよびその他のジェネリックコレクションの ContainsIndexOfLastIndexOf、および Remove メソッドと一致します。This is consistent with the Contains, IndexOf, LastIndexOf, and Remove methods of the Dictionary<TKey,TValue> class and other generic collections.


Equals(T, T)

指定したオブジェクトが等しいかどうかを判断します。Determines whether the specified objects are equal.


指定したオブジェクトのハッシュ コードを返します。Returns a hash code for the specified object.