Tuple(Of T1, T2, T3).IStructuralEquatable.Equals Method (Object, IEqualityComparer)

 
System_CAPS_noteNote

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Returns a value that indicates whether the current Tuple(Of T1, T2, T3) object is equal to a specified object based on a specified comparison method.

Namespace:   System
Assembly:  mscorlib (in mscorlib.dll)

Private Function Equals (
	other As Object,
	comparer As IEqualityComparer
) As Boolean
	Implements IStructuralEquatable.Equals

Parameters

other
Type: System.Object

The object to compare with this instance.

comparer
Type: System.Collections.IEqualityComparer

An object that defines the method to use to evaluate whether the two objects are equal.

Return Value

Type: System.Boolean

true if the current instance is equal to the specified object; otherwise, false.

This member is an explicit interface member implementation. It can be used only when the Tuple(Of T1, T2, T3) instance is cast to an IStructuralEquatable interface.

The IEqualityComparer.Equals implementation is called only if other is not null, and if it can be successfully cast (in C#) or converted (in Visual Basic) to a Tuple(Of T1, T2, T3) object whose components are of the same types as the current instance. The Tuple(Of T1, T2, T3).IStructuralEquatable.Equals method first passes the Item1 values of the Tuple(Of T1, T2, T3) objects to be compared to the IEqualityComparer.Equals implementation. If this method call returns true, the method is called again and passed the Item2 values of the two Tuple(Of T1, T2, T3) objects. If this method call returns true again, the method is called a third time and passed the Item3 values of the two Tuple(Of T1, T2, T3) objects.

The following example defines an Item2Comparer class that implements the IEqualityComparer interface and changes the way in which Tuple(Of T1, T2, T3) objects are evaluated for equality. The method always returns true when it is passed the Item1 property values of two Tuple(Of T1, T2, T3) objects, and it calls the Tuple(Of T1, T2, T3).IStructuralEquatable.Equals method to evaluate their Item2 property values. If this method call returns true, their Item3 property values are passed to the method, which always returns true. As a result, the method tests for equality based only on the value of the Item2 property. The output illustrates the result for a data set of Tuple(Of T1, T2, T3) objects that record the names, mean test score, and number of tests of students in a class.

Imports System.Collections

Public Class Item2Comparer(Of T1, T2, T3) : Implements IEqualityComparer

   Public Overloads Function Equals(x As Object, y As Object) As Boolean _
                   Implements IEqualityComparer.Equals
      ' Return true for all values of Item1.
      If TypeOf x Is T1 Then
         Return True
      ElseIf TypeOf x Is T2 Then
         Return x.Equals(y)
      Else
         Return True
      End If
   End Function

   Public Overloads Function GetHashCode(obj As Object) As Integer _
                    Implements IEqualityComparer.GetHashCode
      If TypeOf obj Is T1 Then
         Return CType(obj, T1).GetHashCode()
      ElseIf TypeOf obj Is T2 Then
         Return CType(obj, T2).GetHashCode()
      Else	
         Return CType(obj, T3).GetHashCode()
      End If   
   End Function                
End Class

Module Example
   Public Sub Main()
      Dim scores() = 
                { Tuple.Create("Ed", 78.8, 8),
                  Tuple.Create("Abbey", 92.1, 9), 
                  Tuple.Create("Jim", 71.2, 9),
                  Tuple.Create("Sam", 91.7, 8), 
                  Tuple.Create("Sandy", 71.2, 5),
                  Tuple.Create("Penelope", 82.9, 8),
                  Tuple.Create("Serena", 71.2, 9),
                  Tuple.Create("Judith", 84.3, 9) }

      For ctr As Integer = 0 To scores.Length - 1
         Dim score As IStructuralEquatable = scores(ctr)
         For ctr2 As Integer = ctr + 1 To scores.Length - 1
            Console.WriteLine("{0} = {1}: {2}", score, 
                              scores(ctr2), 
                              score.Equals(scores(ctr2), 
                                           new Item2Comparer(Of String, Double, Integer)))
         Next
         Console.WriteLine()
      Next                     
   End Sub
End Module
' The example displays the following output:
'      (Ed, 78.8, 8) = (Abbey, 92.1, 9): False
'      (Ed, 78.8, 8) = (Jim, 71.2, 9): False
'      (Ed, 78.8, 8) = (Sam, 91.7, 8): False
'      (Ed, 78.8, 8) = (Sandy, 71.2, 5): False
'      (Ed, 78.8, 8) = (Penelope, 82.9, 8): False
'      (Ed, 78.8, 8) = (Serena, 71.2, 9): False
'      (Ed, 78.8, 8) = (Judith, 84.3, 9): False
'      
'      (Abbey, 92.1, 9) = (Jim, 71.2, 9): False
'      (Abbey, 92.1, 9) = (Sam, 91.7, 8): False
'      (Abbey, 92.1, 9) = (Sandy, 71.2, 5): False
'      (Abbey, 92.1, 9) = (Penelope, 82.9, 8): False
'      (Abbey, 92.1, 9) = (Serena, 71.2, 9): False
'      (Abbey, 92.1, 9) = (Judith, 84.3, 9): False
'
'      (Jim, 71.2, 9) = (Sam, 91.7, 8): False
'      (Jim, 71.2, 9) = (Sandy, 71.2, 5): True
'      (Jim, 71.2, 9) = (Penelope, 82.9, 8): False
'      (Jim, 71.2, 9) = (Serena, 71.2, 9): True
'      (Jim, 71.2, 9) = (Judith, 84.3, 9): False
'
'      (Sam, 91.7, 8) = (Sandy, 71.2, 5): False
'      (Sam, 91.7, 8) = (Penelope, 82.9, 8): False
'      (Sam, 91.7, 8) = (Serena, 71.2, 9): False
'      (Sam, 91.7, 8) = (Judith, 84.3, 9): False
'
'      (Sandy, 71.2, 5) = (Penelope, 82.9, 8): False
'      (Sandy, 71.2, 5) = (Serena, 71.2, 9): True
'      (Sandy, 71.2, 5) = (Judith, 84.3, 9): False
'
'      (Penelope, 82.9, 8) = (Serena, 71.2, 9): False
'      (Penelope, 82.9, 8) = (Judith, 84.3, 9): False
'
'      (Serena, 71.2, 9) = (Judith, 84.3, 9): False

Universal Windows Platform
Available since 8
.NET Framework
Available since 4.0
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 4.0
Windows Phone Silverlight
Available since 8.0
Windows Phone
Available since 8.1
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