EqualityComparer<T>.Default プロパティ
定義
汎用引数で指定された型に対して、等値であるかどうかを比較するための既定の比較子を返します。Returns a default equality comparer for the type specified by the generic argument.
public:
static property System::Collections::Generic::EqualityComparer<T> ^ Default { System::Collections::Generic::EqualityComparer<T> ^ get(); };
public static System.Collections.Generic.EqualityComparer<T> Default { get; }
member this.Default : System.Collections.Generic.EqualityComparer<'T>
Public Shared ReadOnly Property Default As EqualityComparer(Of T)
プロパティ値
T
型の EqualityComparer<T> クラスの既定のインスタンス。The default instance of the EqualityComparer<T> class for type T
.
例
次の例では、型の要素を含むコレクションを作成 Box
し、 FindFirst
メソッドを2回呼び出して、別のボックスと一致するボックスを検索します。The following example creates a collection that contains elements of the Box
type and then searches it for a box matching another box by calling the FindFirst
method, twice.
最初の検索では、等値比較子が指定されていません。つまり、を使用して、 FindFirst
EqualityComparer<T>.Default ボックスが等しいかどうかを判断します。The first search does not specify any equality comparer, which means FindFirst
uses EqualityComparer<T>.Default to determine equality of boxes. さらに、クラスのメソッドの実装を使用し IEquatable<T>.Equals Box
ます。That in turn uses the implementation of the IEquatable<T>.Equals method in the Box
class. 2つのボックスは、ディメンションが同じである場合に等しいと見なされます。Two boxes are considered equal if their dimensions are the same.
2番目の検索では、ボリュームごとの等価性を定義する等値比較子 () を指定し BoxEqVolume
ます。The second search specifies an equality comparer (BoxEqVolume
) that defines equality by volume. 2つのボックスは、ボリュームが同じである場合に等しいと見なされます。Two boxes are considered equal if their volumes are the same.
using System;
using System.Collections.Generic;
static class Program
{
static void Main()
{
var redBox = new Box(8, 8, 4);
var blueBox = new Box(6, 8, 4);
var greenBox = new Box(4, 8, 8);
var boxes = new[] { redBox, blueBox, greenBox };
var boxToFind = new Box(4, 8, 8);
var foundByDimension = boxes.FindFirst(boxToFind);
Console.WriteLine($"Found box {foundByDimension} by dimension.");
var foundByVolume = boxes.FindFirst(boxToFind, new BoxEqVolume());
Console.WriteLine($"Found box {foundByVolume} by volume.");
}
}
public static class CollectionExtensions
{
public static T FindFirst<T>(
this IEnumerable<T> collection, T itemToFind, IEqualityComparer<T> comparer = null)
{
comparer = comparer ?? EqualityComparer<T>.Default;
foreach (var item in collection)
{
if (comparer.Equals(item, itemToFind))
{
return item;
}
}
throw new InvalidOperationException("No matching item found.");
}
}
public class BoxEqVolume : EqualityComparer<Box>
{
public override bool Equals(Box b1, Box b2)
{
if (object.ReferenceEquals(b1, b2))
return true;
if (b1 is null || b2 is null)
return false;
return b1.Volume == b2.Volume;
}
public override int GetHashCode(Box box) => box.Volume.GetHashCode();
}
public class Box : IEquatable<Box>
{
public Box(int height, int length, int width)
{
this.Height = height;
this.Length = length;
this.Width = width;
}
public int Height { get; }
public int Length { get; }
public int Width { get; }
public int Volume => Height * Length * Width;
public bool Equals(Box other)
{
if (other is null)
return false;
return this.Height == other.Height && this.Length == other.Length
&& this.Width == other.Width;
}
public override bool Equals(object obj) => Equals(obj as Box);
public override int GetHashCode() => (Height, Length, Width).GetHashCode();
public override string ToString() => $"{Height} x {Length} x {Width}";
}
/* This example produces the following output:
*
Found box 4 x 8 x 8 by dimension.
Found box 8 x 8 x 4 by volume.
*/
Imports System.Collections.Generic
Imports System.Runtime.CompilerServices
Public Class Example
Public Shared Sub Main()
Dim redBox As New Box(8, 8, 4)
Dim blueBox As New Box(6, 8, 4)
Dim greenBox As New Box(4, 8, 8)
Dim boxes As Box() = { redBox, blueBox, greenBox }
Dim boxToFind As New Box(4, 8, 8)
Dim foundByDimension = boxes.FindFirst(boxToFind)
Console.WriteLine($"Found box {foundByDimension} by dimension.")
Dim foundByVolume = boxes.FindFirst(boxToFind, New BoxEqVolume())
Console.WriteLine($"Found box {foundByVolume} by volume.")
End Sub
Private Shared Sub PrintBoxCollection(boxes As Dictionary(Of Box, String))
For Each kvp As KeyValuePair(Of Box, String) In boxes
Console.WriteLine($"{kvp.Key.Height} x {kvp.Key.Length} x {kvp.Key.Width} - {kvp.Value}")
Next
End Sub
End Class
Public Module CollectionExtensions
<Extension()>
Public Function FindFirst(Of T)(
collection As IEnumerable(Of T), itemToFind As T, Optional comparer As IEqualityComparer(Of T) = Nothing)
comparer = If(comparer, EqualityComparer(Of T).Default)
For Each item In collection
If comparer.Equals(item, itemToFind)
Return item
End IF
Next
Throw New InvalidOperationException("No matching item found.")
End Function
End Module
Public Class BoxEqVolume
Inherits EqualityComparer(Of Box)
Public Overrides Function GetHashCode(box As Box) As Integer
Return box.Volume.GetHashCode()
End Function
Public Overrides Function Equals(b1 As Box, b2 As Box) As Boolean
If b1 Is b2 Then
Return True
End If
If b1 Is Nothing OrElse b2 Is Nothing Then
Return False
End If
Return b1.Volume = b2.Volume
End Function
End Class
Public Class Box
Implements IEquatable(Of Box)
Public Sub New(height As Integer, length As Integer, width As Integer)
Me.Height = height
Me.Length = length
Me.Width = width
End Sub
Public ReadOnly Property Height() As Integer
Public ReadOnly Property Length() As Integer
Public ReadOnly Property Width() As Integer
Public ReadOnly Property Volume() As Integer
Get
Return Height * Length * Width
End Get
End Property
Public Overloads Function Equals(other As Box) As Boolean Implements IEquatable(Of Box).Equals
If other Is Nothing Then
Return False
End If
Return Me.Height = other.Height AndAlso Me.Length = other.Length AndAlso
Me.Width = other.Width
End Function
Public Overrides Function Equals(other As Object) As Boolean
Return Equals(TryCast(other, Box))
End Function
Public Overrides Function GetHashCode() As Integer
Return (Height, Length, Width).GetHashCode()
End Function
Public Overrides Function ToString() As String
Return $"{Height} x {Length} x {Width}"
End Function
End Class
' This example produces the following output:
'
' Found box 4 x 8 x 8 by dimension.
' Found box 8 x 8 x 4 by volume.
注釈
プロパティは、 Default 型がインターフェイスを実装しているかどうかを確認し、存在する場合は、 T
System.IEquatable<T> EqualityComparer<T> その実装を使用するを返します。The Default property checks whether type T
implements the System.IEquatable<T> interface and, if so, returns an EqualityComparer<T> that uses that implementation. それ以外の場合は、 EqualityComparer<T> によって提供されるおよびのオーバーライドを使用するを返し Object.Equals Object.GetHashCode T
ます。Otherwise, it returns an EqualityComparer<T> that uses the overrides of Object.Equals and Object.GetHashCode provided by T
.