What can get destroyed in your settlements?

So far, nothing in my settlement (I favour the Starlight Drive-In) has been destroyed, but I've heard mention (in this question) of things getting destroyed in a settlement during an attack. Is there a list of those vulnerable objects? Is it limited to "items" like generators and people, or can walls and other "building" structures be destroyed?

Thanks!

As discussed in this question, it's not so much "destroyed" as it is "damaged to 0 durability". It seems that this damage is limited to defences (guard towers and turrets) along with resource generation (crops, water pumps, generators).