Messages and methods
All computation is initiated by messages.
A message can get or set the value of a data slot, or invoke a
method, which can send more messages.
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Messages and methods
In Self, all computation is initiated by messages. A message can result in
an atomic action, such as getting the value of a data slot or assigning a value to an
assignable slot, or can cause a method to be executed. In turn, the method may
contain further message sends.
We can try sending messages to the account using an evaluator. To get an evaluator
for an object, we use the middle-button (yellow) menu on the title bar of the object.
Any expression we enter in the evaluator will be evaluated in the context of the
object (i.e., with self bound to the object itself) by clicking on the evaluate button.
For example:
- balance
-
returns the current balance
- deposit: n
-
increases the balance by n.
- withdraw: n
-
decreases the balance by n, to a limit of zero.
Every evaluation has a result object. The result of the deposit; and withdraw:
messages is the bank account object itself. The result, if different from the host of
the evaluation, becomes attached to the cursor. We sometimes call the cursor the
hand, and say the object is in the hand. You can drop an object that is in the hand by
clicking the left button. If the evaluation results in the receiver object itself, rather than attaching to the hand, it wiggles slightly.
If you're not interested in the result of the evaluation, you can use the `Do
selection' middle-button menu item in the evaluator to evaluate the selected
expression but ignore the result.
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