Writing a Single Element Operator

The role of a single element operator is to add an extension method to any type that implements IEnumerable<T> and return a single element from that collection. The built-in standard query operators First, Last and ElementAt are examples of this category of operator, returning the first element, the last element, or the element at a given index position, respectively.

Understanding how Microsoft constructed the standard query operators is the first step to understanding how to write custom operators. To explore Microsoft’s approach to operator construction, let’s build our own version of the Last operator before moving onto building a more complex operator.