C# | Getting an enumerator that iterates through HashSet<T>

HashSet<T>.GetEnumerator Method is used to get an enumerator that iterates through a HashSet object.

Syntax:

public System.Collections.Generic.HashSet<T>.Enumerator GetEnumerator ();

Return Value: It returns a HashSet<T>.Enumerator object for the HashSet<T> object.

Below programs illustrate the use of above-discussed method:

Example 1:

// C# code to get an enumerator that
// iterates through the HashSet<T>
using System;
using System.Collections.Generic;

class GFG {

    // Driver code
    public static void Main()
    {

        // Creating a HashSet<T> of strings
        HashSet<string> mySet = new HashSet<string>();

        // Inserting elements in HashSet
        mySet.Add("DS");
        mySet.Add("C++");
        mySet.Add("Java");
        mySet.Add("C#");

        // To get an Enumerator
        // for the HashSet<T>.
        HashSet<string>.Enumerator em = mySet.GetEnumerator();
        display(em);
    }

    // display method
    static void display(IEnumerator<string> em)
    {
        while (em.MoveNext()) {
            string val = em.Current;
            Console.WriteLine(val);
        }
    }
}

Output:

DS
C++
Java
C#

Example 2:

// C# code to get an enumerator that
// iterates through the HashSet<T>
using System;
using System.Collections.Generic;

class GFG {

    // Driver code
    public static void Main()
    {

        // Creating a HashSet of integers
        HashSet<int> mySet1 = new HashSet<int>();

        // Inserting elements in HashSet
        for (int i = 1; i <= 10; i++)
            mySet1.Add(2 * i);

        // To get an Enumerator
        // for the HashSet<T>.
        HashSet<int>.Enumerator em = mySet1.GetEnumerator();
        display(em);
    }

    // display method
    static void display(IEnumerator<int> em)
    {
        while (em.MoveNext()) {
            int val = em.Current;
            Console.WriteLine(val);
        }
    }
}

Output:

2
4
6
8
10
12
14
16
18
20

Note:

• The foreach statement of the C# language hides the complexity of the enumerators. Therefore, using foreach is recommended, instead of directly manipulating the enumerator.
• Enumerators can be used to read the data in the collection, but they cannot be used to modify the underlying collection.
• Current returns the same object until either MoveNext or Reset is called. MoveNext sets Current to the next element.
• An enumerator remains valid as long as the collection remains unchanged. If changes are made to the collection, such as adding, modifying, or deleting elements, the enumerator is irrecoverably invalidated and its behavior is undefined.
• This method is an O(1) operation.

Reference:

• https://docs.microsoft.com/en-us/dotnet/api/system.collections.generic.hashset-1.getenumerator?view=netframework-4.7.2