With the basic techniques presented in the preceding
chapters, we're ready do our first real Smalltalk program.
In this chapter we will construct three new types of objects
(known as classes), using the Smalltalk technique of
inheritance to tie the classes together, create new objects
belonging to these classes (known as creating instances of
the class), and send messages to these objects.
We'll exercise all this by implementing a toy home-finance
accounting system. We will keep track of our overall
cash, and will have special handling for our checking
and savings accounts. From this point on, we will be defining
classes which will be used in future chapters. Since
you will probably not be running this whole tutorial in one
Smalltalk session, it would be nice to save off the state of
Smalltalk and resume it without having to retype all the
previous examples. To save the current state of GNU Smalltalk,
type:
ObjectMemory snapshot: 'myimage.im' !
and from your shell, to later restart Smalltalk from this
"snapshot":
$ gst -I myimage.im
Such a snapshot currently takes a little more than a megabyte,
and contains all variables, classes, and definitions you
have added.
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