Finding the Entity and World in populate

The populate function looks like a constructor. It is not quite. Library authors need what is already wired when it runs; game code usually does not.

What is already there

Concord sets self.__entity before populate runs. If that Entity was queued into a World, Entity:getWorld works:

Concord.Component("inRoom", function (c, roomId)
  local entity = c.__entity
  local world = entity:getWorld()
  -- world may be nil if the Entity was constructed with no World
end)

The builtin key is the canonical example: it refuses to populate unless entity:inWorld(), then asks the World to assign a key. Read concord/builtins/key.lua alongside this page.

What is not there yet

The new Component is not on the Entity until populate returns. During a replacing give, entity.position is still the old instance. Do not entity:give("position", ...) from inside position’s populate.

Do not spawn Entities, do not flush, and do not assume Pools already contain you.

When to use this

Game code should prefer assemblages and Systems. Reach for __entity when a Component must register itself with something the World owns: the key hash, a physics world stored as a resource, a spatial index you do not want a System to have to notice.

Tear that registration down in removed. key does this; your Component should too.

See also

• key
• Component:removed Guide
• Components Guide