gistfile1.nim

type RenderTexture = object
type RenderWindow = object
type Sprite = object

type RenderTarget* = RenderTexture | RenderWindow
type RenderTargetProc* = proc(s:Sprite, r:RenderTarget)

type Drawable* = generic d, r
  r is RenderTarget
  d.draw(r)

# ---

proc draw*(s: Sprite, r: RenderTarget) =
  echo "RENDERED"

# ---

var w: RenderWindow
var s: Sprite
s.draw(w)


# --- ORIGINAL BELOW --- #


type RenderTexture = object
type RenderWindow = object
type Sprite = object

type RenderTarget* = RenderTexture | RenderWindow

type Drawable* = generic d
  d.draw(RenderWindow)
  d.draw(RenderTexture)

# ---

proc draw*(obj: Sprite, renderTarget: RenderTarget) =
  echo "RENDERED"

proc draw*(renderTarget: RenderTarget, obj: Drawable) =
  obj.draw(renderTarget)

# ---

var w: RenderWindow
var s: Sprite
w.draw(s)