Multi-methods

Note: Starting from Nim 0.20, to use multi-methods one must explicitly pass --multimethods:on when compiling.

In a multi-method all parameters that have an object type are used for the dispatching:

type
  Thing = ref object of RootObj
  Unit = ref object of Thing
    x: int
method collide(a, b: Thing) {.inline.} =
  quit "to override!"
method collide(a: Thing, b: Unit) {.inline.} =
  echo "1"
method collide(a: Unit, b: Thing) {.inline.} =
  echo "2"
var a, b: Unit
new a
new b
collide(a, b) # output: 2