Warning: This is the manual of the legacy Guile 2.2 series. You may want to read the manual of the current stable series instead.

8.7 Inheritance

Here are some class definitions to help illustrate inheritance:

(define-class A () a)
(define-class B () b)
(define-class C () c)
(define-class D (A B) d a)
(define-class E (A C) e c)
(define-class F (D E) f)

A, B, C have a null list of superclasses. In this case, the system will replace the null list by a list which only contains <object>, the root of all the classes defined by define-class. D, E, F use multiple inheritance: each class inherits from two previously defined classes. Those class definitions define a hierarchy which is shown in Figure 8.2. In this figure, the class <top> is also shown; this class is the superclass of all Scheme objects. In particular, <top> is the superclass of all standard Scheme types.

          <top>
          / \\\_____________________
         /   \\___________          \
        /     \           \          \
    <object>  <pair>  <procedure>  <number>
    /  |  \                           |
   /   |   \                          |
  A    B    C                      <complex>
  |\__/__   |                         |
   \ /   \ /                          |
    D     E                         <real>
     \   /                            |
       F                              |
                                   <integer>

When a class has superclasses, its set of slots is calculated by taking the union of its own slots and those of all its superclasses. Thus each instance of D will have three slots, a, b and d). The slots of a class can be discovered using the class-slots primitive. For instance,

(class-slots A) ⇒ ((a))
(class-slots E) ⇒ ((a) (e) (c))
(class-slots F) ⇒ ((e) (c) (b) (d) (a) (f))

The ordering of the returned slots is not significant.