Items and an empty answer

How much copper is in a block — and how "there is none of it" differs from "the question does not apply"

mediumYou need: sensor: properties of buildings, Emptiness: null

As its third argument sensor takes not only a property but also an item. The vault holds 220 copper and 15 graphite; there is no silicon at all, and a vault does not hold water in principle.

steptick 0

Sensor0

=

 in

Sensor1

=

 in

Sensor2

=

 in

Sensor3

=

 in

@counter0number

coppernullnull

siliconnullnull

waternullnull

firstnullnull

Three answers to three similar questions:

Asked	Answer	What it means
@copper	220	the item is there, and here is how much
@silicon	0	the item exists, but not here — zero means “none”
@water	null	a vault does not hold liquids at all — the question does not apply

Silent failure

In an ordinary comparison null equals zero, so a check for “no copper left” fires on “no block” and “wrong property” too. What to do about that is in the lesson «Emptiness: null».

The first item is an object

@firstItem gives not a count but the item itself: the same object as the constant @copper. It is convenient to pass on — into ucontrol itemTake, into sensor as the next argument, into print.

“First” means the one that has been in the block longest and has not run out, not the largest and not the first alphabetically. On a drill it is whatever it is mining.

What can be asked as an item

Any item and any liquid in the game: @copper, @graphite, @water, @cryofluid. The full list is in the reference, along with a way to walk them all by index.

Note

The course sandbox has no liquids: the blocks that hold them are always empty. The numbers about items are real, the ones about liquids are not.

Remember

• As its third field sensor takes not only a property but also an item or a liquid.
• “There is none of the item” is zero; “the question does not apply” is null.
• @firstItem gives the item itself as an object, not its count.

Task

Click the pencil by the property in any line and ask the vault for three more things: @graphite (it is there), @titanium (not in this vault, but it exists as an item) and @sand. The first answers with a number, the others with zero.

Then type @vault into the block’s field instead of vault1 — ask the same thing of the vault’s type rather than of the vault. The answer is not about contents but about price: sensor @vault @titanium gives 250, the amount of titanium a vault costs. A blueprint has no contents but it does have a cost, and this is the only way to learn it from logic.

In infinite-resources mode the price honestly answers zero — just like building, which deducts nothing.