Programming in XPCE/Prolog: Section 7.2

## 7.2 Accessing instance variables (slots)

The method `object`<->`slot' is used to access slots directly, bypassing possible methods with the same name. Normally, it should only be used in `->`initialise (see below) and when defining a method with the same name as a variable. Below is a fragment where a `type` slot is displayed by a text object named `type` in a graphical object. This variable has access `get`, associating a universal method `<-`type that yields the current value of the slot. The implementation of `->`type uses the `->`slot method to write the argument in the `<-`type slot and subsequently performs the required side-effects. The ... indicate where the fragment is incomplete.

    variable(type,  name,   get, "Epistemological type").

    initialise(D, Type:name, ...) :->
            send_super(D, initialise),
            send(D, slot, type, Type),
            send(D, display, new(T, text(Type))),
            send(T, name, type),
            ...

    type(D, Type:type) :->
            "Modify the epistemological type"::
            send(D, slot, type, Type),
            get(D, member, type, Text),
            send(Text, string, Type).

object ->slot: name, unchecked
object <-slot: name
  uncheckedRead or write slot without side-effects. The value will be converted to the type of the instance variable addressed. An error is raised if this conversion is not defined or if the slot does not exist.