When the for..in loop was introduced in Delphi 2005, the concept of enumerable types was also introduced into the Delphi language.

As you know, there are some built-in enumerable types. However, you can create your own enumerable types using a very simple pattern.

To make your container enumerable, implement a single method called GetEnumerator, that must return a reference to an object, interface, or record, that implements the following three methods and one property (in the sample, the element to enumerate is TFoo):

function GetCurrent: TFoo;
function MoveNext: Boolean;
property Current: TFoo read GetCurrent;

There are a lot of samples related to standard enumerable types, so in this recipe you'll look at some not-so-common utilizations.