Article
11/18/2011

Tuple<T1, T2>.IStructuralComparable.CompareTo Method

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Compares the current Tuple<T1, T2> object to a specified object by using a specified comparer, and returns an integer that indicates whether the current object is before, after, or in the same position as the specified object in the sort order.

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

Syntax

'Declaration
Private Function CompareTo ( _
    other As Object, _
    comparer As IComparer _
) As Integer Implements IStructuralComparable.CompareTo

int IStructuralComparable.CompareTo(
    Object other,
    IComparer comparer
)

Parameters

other
Type: System.Object
An object to compare with the current instance.

comparer
Type: System.Collections.IComparer
An object that provides custom rules for comparison.

Return Value

Type: System.Int32
A signed integer that indicates the relative position of this instance and other in the sort order, as shown in the following table.

Value	Description
A negative integer	This instance precedes other.
Zero	This instance and other have the same position in the sort order.
A positive integer	This instance follows other.

Implements

IStructuralComparable.CompareTo(Object, IComparer)

Exceptions

Exception	Condition
ArgumentException	other is not a Tuple<T1, T2> object.

Remarks

This member is an explicit interface member implementation. It can be used only when the Tuple<T1, T2> instance is cast to an IStructuralComparable interface.

Although this method can be called directly, it is most commonly called by collection sorting methods that include IComparer parameters to order the members of a collection, such as the Array.Sort(Array, IComparer) method.

Caution:
The IStructuralComparable.CompareTo method is intended for use in sorting operations. It should not be used when the primary purpose of a comparison is to determine whether two objects are equal. To determine whether two objects are equal, call the IStructuralEquatable.Equals method.

Examples

The following example creates an array of Tuple<T1, T2> objects that consist of a student's name and test score. It displays the component of each tuple in the array in unsorted order, sorts the array, and then calls ToString to display the value of each tuple in sorted order. To sort the array, the example defines a generic ScoreComparer class that implements the IComparer interface and sorts the Tuple<T1, T2> objects in ascending order by the value of their second component rather than their first component. Note that the example does not directly call the IStructuralComparable.CompareTo method. This method is called implicitly by the Array.Sort(Array, IComparer) method for each element in the array.

Imports System.Collections
Imports System.Collections.Generic

Public Class ScoreComparer(Of T1, T2) : Implements IComparer
   Public Function Compare(ByVal x As Object, ByVal y As Object) As Integer _
                   Implements IComparer.Compare
      Dim tX As Tuple(Of T1, T2) = TryCast(x, Tuple(Of T1, T2))
      If tX Is Nothing Then
         Return 0
      Else
         Dim tY As Tuple(Of T1, T2) = DirectCast(y, Tuple(Of T1, T2))
         Return Comparer(Of T2).Default.Compare(tX.Item2, tY.Item2)
      End If
   End Function
End Class

Module Example
   Public Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)
      Dim scores() As Tuple(Of String, Nullable(Of Integer)) = _
                      { New Tuple(Of String, Nullable(Of Integer))("Jack", 78), _
                        New Tuple(Of String, Nullable(Of Integer))("Abbey", 92), _
                        New Tuple(Of String, Nullable(Of Integer))("Dave", 88), _
                        New Tuple(Of String, Nullable(Of Integer))("Sam", 91), _
                        New Tuple(Of String, Nullable(Of Integer))("Ed", Nothing), _
                        New Tuple(Of String, Nullable(Of Integer))("Penelope", 82), _
                        New Tuple(Of String, Nullable(Of Integer))("Linda", 99), _
                        New Tuple(Of String, Nullable(Of Integer))("Judith", 84) }

      outputBlock.Text &= "The values in unsorted order:" & vbCrLf
      For Each score In scores
         outputBlock.Text &= score.ToString() & vbCrLf
      Next
      outputBlock.Text &= vbCrLf

      Array.Sort(scores, New ScoreComparer(Of String, Nullable(Of Integer))())

      outputBlock.Text &= "The values in sorted order:" & vbCrLf
      For Each score In scores
         outputBlock.Text &= score.ToString() & vbCrLf
      Next
   End Sub
End Module
' The example displays the following output;
'       The values in unsorted order:
'       (Jack, 78)
'       (Abbey, 92)
'       (Dave, 88)
'       (Sam, 91)
'       (Ed, )
'       (Penelope, 82)
'       (Linda, 99)
'       (Judith, 84)
'       
'       The values in sorted order:
'       (Ed, )
'       (Jack, 78)
'       (Penelope, 82)
'       (Judith, 84)
'       (Dave, 88)
'       (Sam, 91)
'       (Abbey, 92)
'       (Linda, 99)

using System;
using System.Collections;
using System.Collections.Generic;

public class ScoreComparer<T1, T2> : IComparer
{
   public int Compare(object x, object y)
   {
      Tuple<T1, T2> tX = x as Tuple<T1, T2>;
      if (tX == null)
      {
         return 0;
      }
      else
      {
         Tuple<T1, T2> tY = y as Tuple<T1, T2>;
         return Comparer<T2>.Default.Compare(tX.Item2, tY.Item2);
      }
   }
}

public class Example
{
   public static void Demo(System.Windows.Controls.TextBlock outputBlock)
   {
      Tuple<string, Nullable<int>>[] scores = 
                    { new Tuple<string, Nullable<int>>("Jack", 78),
                      new Tuple<string, Nullable<int>>("Abbey", 92), 
                      new Tuple<string, Nullable<int>>("Dave", 88),
                      new Tuple<string, Nullable<int>>("Sam", 91), 
                      new Tuple<string, Nullable<int>>("Ed", null),
                      new Tuple<string, Nullable<int>>("Penelope", 82),
                      new Tuple<string, Nullable<int>>("Linda", 99),
                      new Tuple<string, Nullable<int>>("Judith", 84) };

      outputBlock.Text += "The values in unsorted order:" + "\n";
      foreach (var score in scores)
         outputBlock.Text += score.ToString() + "\n";

      outputBlock.Text += "\n";

      Array.Sort(scores, new ScoreComparer<string, Nullable<int>>());

      outputBlock.Text += "The values in sorted order:" + "\n";
      foreach (var score in scores)
         outputBlock.Text += score.ToString() + "\n";
   }
}
// The example displays the following output;
//       The values in unsorted order:
//       (Jack, 78)
//       (Abbey, 92)
//       (Dave, 88)
//       (Sam, 91)
//       (Ed, )
//       (Penelope, 82)
//       (Linda, 99)
//       (Judith, 84)
//       
//       The values in sorted order:
//       (Ed, )
//       (Jack, 78)
//       (Penelope, 82)
//       (Judith, 84)
//       (Dave, 88)
//       (Sam, 91)
//       (Abbey, 92)
//       (Linda, 99)

Version Information

Silverlight

Supported in: 5, 4

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

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