gistfile1.nim

type
    App* = ref object of RootObj
        vt*: AppVT

    AppVT = object
        draw*: proc(my:App)
        update*: proc(my:App, dt:float)

var defaultVT = AppVT(
    draw: (proc(my:App) = discard), 
    update: (proc(my:App, dt:float) = discard)
)


## accessors
proc draw* (my:App) {.inline.} = my.vt.draw(my)

## to implement your game state
var myVT = defaultVT
myVT.draw = ...
myVT.update = ...