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


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Returns a value that indicates whether the current Tuple(Of T1) 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


Type: System.Object

The object to compare with this instance.

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) 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) object whose single component is of the same type as the current instance. The method is passed the Item1 component of the current instance and the Item1 component of the Tuple(Of T1) object represented by the other parameter.

The following example defines an IEqualityComparer implementation that considers two floating-point values to be equal if they are approximately equal to each other (that is, if one value is within .01 percent of the other).

Imports System.Collections

Public Class Tuple1Comparer : Implements IEqualityComparer
   Public Overloads Function Equals(x As Object, y As Object) As Boolean _
                   Implements IEqualityComparer.Equals
      ' Check if x is a floating point type. If x is, then y is.
      If TypeOf x Is Double Or TypeOf x Is Single Then   
         ' Convert to Double values.
         Dim dblX As Double = CDbl(x)
         Dim dblY As Double = CDbl(y)
         If Double.IsNan(dblX) Or Double.IsInfinity(dblX) Or _
            Double.IsNan(dblY) Or Double.IsInfinity(dblY) Then
            Return dblX.Equals(dblY)   
            Return Math.Abs(dblX - dblY) <= dblY * .0001
         End If
         Return x.Equals(y)
      End If                    
   End Function

   Public Overloads Function GetHashCode(obj As Object) As Integer _
                   Implements IEqualityComparer.GetHashCode
      Return obj.GetHashCode()
   End Function
End Class

Module Example
   Public Sub Main()
      Dim doubleTuple1 = Tuple.Create(12.3455)

      Dim doubleTuple2 = Tuple.Create(16.8912)
      Dim doubleTuple3 = Tuple.Create(12.3449599)

      ' Compare first tuple with a Tuple(Of Double) with a different value.
      TestEquality(doubleTuple1, doubleTuple2)
      ' Compare first tuple with a Tuple(Of Double) with the same value.
      TestEquality(doubleTuple1, doubleTuple3)
   End Sub

   Private Sub TestEquality(tuple As Tuple(Of Double), obj As Object)
         Console.WriteLine("{0} = {1}: {2}", tuple.ToString(),
                                             DirectCAst(tuple, IStructuralEquatable).Equals(obj, New Tuple1Comparer()))

      Catch e As ArgumentException
         If obj.GetType.IsGenericType Then 
            If obj.GetType().Name = "Tuple`1" Then 
               Console.WriteLine("Cannot compare a Tuple(Of {0}) with a Tuple(Of {1}).", 
                              tuple.Item1.GetType().Name, obj.Item1.GetType().Name)
               Console.WriteLine("Cannot compare a {0} with a {1}.", tuple.GetType().Name, 
            End If
            Console.WriteLine("Cannot compare a {0} with a {1}.", tuple.GetType().Name,
         End If
      End Try
   End Sub
End Module
' The example displays the following output:
'       (12.3455) = (16.8912): False
'       (12.3455) = (12.3449599): True

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