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IStructuralEquatable.Equals Method

Determines whether an object is structurally equal to the current instance.

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

bool Equals(
	Object other,
	IEqualityComparer comparer
)

Parameters

other
Type: System.Object

The object to compare with the current instance.

comparer
Type: System.Collections.IEqualityComparer

An object that determines whether the current instance and other are equal.

Return Value

Type: System.Boolean
true if the two objects are equal; otherwise, false.

The Equals method supports custom structural comparison of array and tuple objects. This method in turn calls the comparer object's IEqualityComparer.Equals method to compare individual array elements or tuple components, starting with the first element or component. The individual calls to IEqualityComparer.Equals end and the IStructuralEquatable.Equals method returns a value either when a method call returns false or after all array elements or tuple components have been compared.

The default equality comparer, EqualityComparer<Object>.Default.Equals, considers two NaN values to be equal. However, in some cases, you may want the comparison of NaN values for equality to return false, which indicates that the values cannot be compared. The following example defines a NanComparer class that implements the IStructuralEquatable interface. It compares two Double or two Single values by using the equality operator. It passes values of any other type to the default equality comparer.

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

public class NanComparer : IEqualityComparer
{
   public new bool Equals(object x, object y)
   {
      if (x is float)
         return (float) x == (float) y;
      else if (x is double)
         return (double) x == (double) y;
      else 
         return EqualityComparer<object>.Default.Equals(x, y);
   }

   public int GetHashCode(object obj)
   {
      return EqualityComparer<object>.Default.GetHashCode(obj);
   }
}

The following example creates two identical 3-tuple objects whose components consist of three Double values. The value of the second component is Double.NaN. The example then calls the Tuple<T1, T2, T3>.Equals method, and it calls the IStructuralEquatable.Equals method three times. The first time, it passes the default equality comparer that is returned by the EqualityComparer<T>.Default property. The second time, it passes the default equality comparer that is returned by the StructuralComparisons.StructuralEqualityComparer property. The third time, it passes the custom NanComparer object. As the output from the example shows, the first three method calls return true, whereas the fourth call returns false.

public class Example
{
   public static void Main()
   {
      var t1 = Tuple.Create(12.3, Double.NaN, 16.4);
      var t2 = Tuple.Create(12.3, Double.NaN, 16.4);

      // Call default Equals method.
      Console.WriteLine(t1.Equals(t2));

      IStructuralEquatable equ = t1;
      // Call IStructuralEquatable.Equals using default comparer.
      Console.WriteLine(equ.Equals(t2, EqualityComparer<object>.Default));

      // Call IStructuralEquatable.Equals using  
      // StructuralComparisons.StructuralEqualityComparer.
      Console.WriteLine(equ.Equals(t2, 
                        StructuralComparisons.StructuralEqualityComparer));

      // Call IStructuralEquatable.Equals using custom comparer.
      Console.WriteLine(equ.Equals(t2, new NanComparer()));
   }
}
// The example displays the following output: 
//       True 
//       True 
//       True 
//       False

.NET Framework

Supported in: 4.6, 4.5, 4

.NET Framework Client Profile

Supported in: 4

Portable Class Library

Supported in: Portable Class Library

Supported in: Windows Phone 8.1

Supported in: Windows Phone Silverlight 8.1

Supported in: Windows Phone Silverlight 8
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