Idio Object System

Idio uses a variant of Gregor Kiczales TinyCLOS itself a simplified version of the Common Lisp Object System.

In the Idio Object System (IOS) classes have super-classes and slots (or fields) in a familiar way, however, the functions that operate on classes are not elements of the classes but are, so-called, generic functions which will can be applied to any set of arguments.

You then define methods, tied to the generic function by name, which declare that for given parameter classes, use this method.

IOS supports multiple dispatch (aka multimethods) where all of the arguments are relevant to the choice of method not just one.

Let’s try the SpaceObject collision example from the Wikipedia multiple dispatch page:

multiple-dispatch.idio
import object

;; no superclass
define-class SpaceObject

define-class Asteroid SpaceObject (size)

define-class Spaceship SpaceObject (size)

;; very terse methods returning a string!
define-method (collide-with (o1 Asteroid)  (o2 Spaceship)) "a/s"
define-method (collide-with (o1 Spaceship) (o2 Asteroid))  "s/a"
define-method (collide-with (o1 Spaceship) (o2 Spaceship)) "s/s"
define-method (collide-with (o1 Asteroid)  (o2 Asteroid))  "a/a"

define-method (collide (o1 SpaceObject) (o2 SpaceObject)) {
  if (and ((slot-ref o1 'size) gt 100)
          ((slot-ref o2 'size) gt 100)) "Big boom!" (collide-with o1 o2)
}

so1 := make-instance Asteroid :size 101
so2 := make-instance Spaceship :size 300

printf "collide so1 so2: %s\n" (collide so1 so2)

so3 := make-instance Asteroid :size 10
so4 := make-instance Spaceship :size 10

printf "collide so3 so4: %s\n" (collide so3 so4)

so5 := make-instance Spaceship :size 101
so6 := make-instance Spaceship :size 10

printf "collide so5 so6: %s\n" (collide so5 so6)

The output has been edited for readability:

$ idio multiple-dispatch
collide so1 so2: Big boom!
collide so3 so4: a/s
collide so5 so6: s/s

Last built at 2024-05-19T06:11:37Z+0000 from 77077af (dev) for Idio 0.3