GetEnumerator

GetEnumerator is a method used to obtain an enumerator for iterating over a collection in .NET languages such as C#. It is defined by the non-generic IEnumerable interface and its generic counterpart IEnumerable<T>, and it is central to the standard iteration pattern in the framework.

The non-generic GetEnumerator returns an IEnumerator, while the generic version returns an IEnumerator<T>. An enumerator provides a MoveNext method to advance the position, a Current property to read the current element, and a Reset method to reset the iteration. Reset is optional in practice, and many implementations throw NotSupportedException if it is called.

In C#, foreach uses GetEnumerator behind the scenes to enumerate the elements of a collection. A type is typically considered enumerable if it implements IEnumerable or IEnumerable<T>. The language also supports pattern-based enumeration: a public GetEnumerator method returning a suitable type with MoveNext and Current can enable foreach without requiring the type to implement the interfaces explicitly.

Common collection types, such as List<T>, arrays, and Dictionary<TKey, TValue>, implement IEnumerable and/or IEnumerable<T>, and their GetEnumerator returns an appropriate enumerator type that yields the elements or key-value pairs. The GetEnumerator method thus enables language-integrated constructs and query operators to work with the collection.

In summary, GetEnumerator is a key part of the .NET enumeration pattern, enabling standard iteration and integration with foreach and LINQ across both generic and non-generic collections.