# Components ---- No need to register!
type
  Position = ref object
    x, y: int

  Velocity = ref object
    x, y: int

let world = World.new()

# Entity
let
  ball = world.create()

# Attaching components
ball
  .attach(
    Position(x: 0, y: 0)
  ).attach(
    Velocity(x: 5, y: 2)
  )

# You can define system using procedure syntax
proc moveSystem(All: [Position, Velocity]) {.system.} =
  for pos, vel in each(entities, [Position, Velocity]):
    pos.x += vel.x
    pos.y += vel.y

proc showPositionSystem(All: [Position]) {.system.} =
  for pos in each(entities, [Position]):
    echo "x: ", pos.x
    echo "y: ", pos.y

# Register systems to world
world.registerSystem(moveSystem)
world.registerSystem(showPositionSystem)

for i in 0..<10:
  world.runSystems()

nimble install https://github.com/glassesneo/ecslib