Ensuring one summoned unit...

I found something else that I would find fair for any hero that can summon multiple units. If a hero already has a summoned unit on the map, and if they summon another unit, then the first would dissapear. I would be able to do this if all of the summon spells were all based on the same thing, but they aren't.

In other words, I'm was wondering if there was a way to make a trigger that checks to see when a hero summons a unit, it will check to see if the hero has any summoned units already, then "replaces" that unit with the new one. If not, then the spell proceeds as normal.

Does anyone have any ideas of how to do this?

Sorry to bother you guys with all of these "Summons" questions, but I wanted to find a new way to use Summons in Warcraft(I'm adopting the summons attribute system from Final Fantasy X, where when the caster gets stronger, the summons do as well).

Simplest method, whenever a hero summons a unit, pick all summoned units owned by the owner of the hero and kill them. Problem: you can't have more than one hero per player this way. In order to store summoned units for multiple heroes per player, you would need either an array structure or a system like the attachable vars.

Thanks, Anitarf. I'll put this in my handy notes.