The "Where" extension method above is an example of compiling a Lambda expression to a code delegate (meaning it compiles down to IL that is callable in the form of a delegate).  The "Where()" extension method to support filtering any IEnumerable collection like above could be implemented using the extension method code below:

Listing 6

The Where() extension method above is passed a filter parameter of type Func<T, bool>, which is a delegate that takes a method with a single parameter of type "T" and returns a boolean indicating whether a condition is met.  When we pass a Lambda expression as an argument to this Where() extension method, the C# compiler will compile our Lambda expressions to be an IL method delegate (where the <T> type will be a Person) that our Where() method can then call to evaluate whether a given condition is met.