_World = {}
World = {}

function World.add(entity)
    _World[entity.id] = entity
    return World
end

function World.foreach(f)
    for id, entity in pairs(_World) do
        f(entity)
    end
end

function World.cull_the_dead()
    to_reap = {}
    for id, e in pairs(_World) do
        if (e.life_time ~= nil and e.life_time <= 0) then
            to_reap[id] = e
        end
    end
    for id, e in pairs(to_reap) do
        _World[id] = nil
    end
    return _World
end

function World.get(id)
    return _World[id]
end