What is the purpose of the C# yield keyword?

The yield keyword in C# is used to define an iterator method that can pause and resume execution during method execution, returning elements of a sequence. The purpose of the yield keyword is to allow a method to generate elements of a sequence on-demand, without needing to generate all elements at once during method execution.

Methods defined using the yield keyword are known as iterator methods, which return an object that implements the IEnumerable and IEnumerator interfaces. This object can be used to access elements in a sequence one by one. Each time the iterator object calls the MoveNext() method, the iterator method resumes execution from where it last paused until it encounters the yield keyword to pause again. The iterator method can generate an element each time MoveNext() is called and return that element using the yield return statement. When the iterator method finishes executing or calls the yield break statement, the iterator object will no longer produce elements.

Using the yield keyword allows for a more concise and efficient way of iterating and accessing sequences. It can reduce memory usage, enhance performance, and make the code easier to read and maintain.