GetElementsByType()

Here is one way...

SuperStrict

Framework BRL.Map
Import BRL.LinkedList
Import BRL.StandardIO

Type TElement

	Const TYPE_PLAYER:Int = 1
	Const TYPE_ENEMY:Int = 2
	Const TYPE_BULLET:Int = 3

	Global golElements:TMap = New TMap
	
	Method Init()
		Local id:String = GetId()
		Local list:TList = TList(golElements.ValueForKey(id))
		If Not list Then
			list = New TList
			golElements.Insert(id, list)
		End If
		
		list.AddLast(Self)
	End Method
	
	Function GetElementsByType:TList(typeId:Int)
		' can return Null TList
		Return TList(golElements.ValueForKey(String(typeId)))
	End Function

	Method GetId:Int() Abstract	
End Type

Type TPlayer Extends TElement

	Method New()
		Init()
	End Method

	'.. create function etc.
	
	Method GetId:Int()
		Return TYPE_PLAYER
	End Method	
	
End Type

Type TEnemy Extends TElement

	Method New()
		Init()
	End Method

	'.. create function etc.

	Method GetId:Int()
		Return TYPE_ENEMY
	End Method	
End Type

Type TBullet Extends TElement

	Method New()
		Init()
	End Method

	'.. create function etc.

	Method GetId:Int()
		Return TYPE_BULLET
	End Method	
End Type


'receive all bullets:
Local olBullets:TList = TElement.GetElementsByType(TElement.TYPE_BULLET)
If olBullets Then
	Print olBullets.count()
End If

New TBullet
New TBullet

olBullets = TElement.GetElementsByType(TElement.TYPE_BULLET)
Print olBullets.count()

If you want all types, you could implement some extra functionality in GetElementsByType().
One advantage to this, is that your type lists are already built, so access of those is faster.
It depends what information you need more often.