export property Pool<T> {
  items: []T = null
}
function grow<T>(p: Pool<T>) -> void {
  if p.items == null { p.items = new []T }
}
export function pool_add<T>(p: Pool<T>, x: T) -> void {
  grow(p)
  push(p.items, x)
}
export function pool_len<T>(p: Pool<T>) -> int { return len(p.items) }