why would you do that?
example - you have these 3 sprites - walls, enemies, player. you have 10 instances of walls, 5 of enemies, 1 of player.
why would you pick each of these instances (including walls) which have var boo ? why would wall even need to be picked ? (in example where you want to check all enemies and yourself)
best would be to use family if you really want all instances, but that family will contain every sprite. it seems wrong whatever you are doing