7.5.3 Defining new classes of frame

7.5.3.1 Specifying slots for a new class of frame

As with any other Dylan class, you can use standard slot options to define slots for any new class of frame. This includes techniques such as setting default values, specifying init-keyword names, and specifying whether or not an init-keyword is required.

The following example defines a subclass of <simple-frame> that defines an additional slot that can be set to a date and time. The default value of the slot is set to the current date and time using an init expression. So that you can provide an initial value for the slot, it is defined with an init-keyword of the same name.

define frame <date-frame> (<simple-frame>)
  slot date :: <date> = current-date(),
    init-keyword: date:;
 // Other stuff here
end class <date-frame>;