IEnumerable VS IEnumerator in C#

Introduction

First let's see a small demonstration of both of these interfaces and then we will talk about the differences.

DEMO

Create a new console application and in the main method add the following.

static void Main(string[] args)
{  
   List<string> Month = new List<string>();  
   Month.Add("January");  
   Month.Add("February");  
   Month.Add("March");  
   Month.Add("April");  
   Month.Add("May");  
   Month.Add("June");  
   Month.Add("July");  
   Month.Add("August");  
   Month.Add("September");  
   Month.Add("October");  
   Month.Add("November");  
   Month.Add("December");  
} 

In our main method, we created a new list collection “Month” of type string. In this collection we added all the 12 months as items in this list.

Note: The List class is present in the System.Collections.Generic namespace.

Now let's create a very simple IEnumerable on this list.

//create IEnumerable of string 
IEnumerable<string> iEnumerableOfString = (IEnumerable<string>)Month;  
  
//If we want to retrieve all the items from this IEnumerable object, we can use a foreach loop. 
foreach(string AllMonths in iEnumerableOfString)
{  
   Console.WriteLine(AllMonths);  
}

Run the application.

We got the list of months.

Now let's see how to do the same, using an IEnumerator and then we will see the differences.

//Create IEnumerator of string.
 
IEnumerator<string> iEnumeratorOfString = Month.GetEnumerator();//to convert list into IEnumerator we can invoke the GetEnumerator method  
  
//To retrieve all the items from the above IEnumerator object, we cannot use foreach loop instead of that we need to invoke MoveNext() Boolean method.  
while(iEnumeratorOfString.MoveNext())
{  
  
}

To display the items on the console window we need to invoke the Current property as in the following:

while(iEnumeratorOfString.MoveNext())  
{  
   Console.WriteLine(iEnumeratorOfString.Current);  
}

Run the application.

Similarities

Both of these interfaces help to loop through the collection.

So, now the next question is, what should I use?

As we know, both of these interfaces give the same result. But if you watch the syntax for IEnumerable, it is very simple.

foreach(string AllMonths in iEnumerableOfString)  
{  
   Console.WriteLine(AllMonths);  
}

But in the case of IEnumerator, we need to invoke the MoveNext method and to retrieve the current item, we need to invoke the current property.

Relation

The IEnumerable interface actually uses IEnumerator. The main reason to create an IEnumerable is to make the syntax shorter and simpler.

If you go to the definition of the IEnumerable<T> interface, you will see this interface has a method GetEnumerator() that returns an IEnumerator object back.