What ways implement the IEnumerable interface in the programming language?

In C# language, the IEnumerable interface is implemented by classes and structures that provide a GetEnumerator() method returning an object that implements the IEnumerator interface. This allows iterating over a collection using a foreach loop.

Main ways to implement IEnumerable:

1. Manual implementation:

public class MyCollection : IEnumerable
{
    private object[] items = {1, 2, 3};

    public IEnumerator GetEnumerator()
    {
        for (int i = 0; i < items.Length; i++)
            yield return items[i];
    }
}

2. Implementation of the generic interface IEnumerable<T>:

public class MyCollection<T> : IEnumerable<T>
{
    private T[] items;

    public MyCollection(T[] items) { this.items = items; }

    public IEnumerator<T> GetEnumerator()
    {
        for (int i = 0; i < items.Length; i++)
            yield return items[i];
    }

    IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
}

3. Using collections from the standard library that already implement IEnumerable (e.g., List<T>, Array).

Thus, the key point is to provide a GetEnumerator() method that returns an enumerator for traversing the collection elements.