Notice that the answer is printed as true or false . So they're very useful for answers to yes or no questions, like the ones we just posed. A dictionary is a special kind of collection. With a regular array, you must index it with integers. With dictionaries, you can index it with any object at all.
Dictionaries thus provide a very powerful way of correlating one piece of information to another.
Their only downside is that they are somewhat less efficient than simple arrays. This fills our dictionary in with some data. Notice how we were able to specify not only integers but also strings as both the key and the value. Smalltalk complains because y is an unknown variable. This is one of those simple questions whose answer runs surprisingly deep.