Not everyone has every property

Why only a turret has @ammo and only a drill has @progress, and how a block's type differs from a building

mediumYou need: sensor: properties of buildings, sensor: items and null

There are 77 properties, and nobody has all of them at once. That is not a limit of logic but how the game is built: a property is read by the code of a particular class, and @ammo is written in the turret, @progress in the drill and the factory, @memoryCapacity in the memory cell. The others simply do not have that code.

steptick 0

Sensor0

=

 in

Sensor1

=

 in

Sensor2

=

 in

Sensor3

=

 in

@counter0number

fullnullnull

currentnullnull

cellSizenullnull

routerSizenullnull

Here a duo is damaged down to 120 out of 250, and the cell has memory while the router does not.

A type is asked about price

That a type and a building are different correspondents was already said in the lesson «Properties of buildings»: @duo is a blueprint, duo1 is a turret on the map. The example’s first two lines ask them the same thing and get different answers: 250 health on the blueprint against 120 on the damaged turret.

Then come the things a building does not have at all: a type has @id and @name, and also a price.

Ask a type for an item rather than a property and you get the build cost: @duo costs 35 copper, @vault 250 titanium. The same question to a building means “how much is inside”, and to a type “how much it costs”. There is no other way to learn a price from logic; in infinite-resources mode it goes to zero.

Who answers what

Common to every building: health, coordinates, team, size, contents. After that it gets specific:

Property	Who has it
@ammo, @ammoCapacity, @currentAmmoType	turrets, 26 blocks
@progress	everything that does work over time: drills, factories, construction
@heat	reactors, heaters, the force projector, power turrets — 25 blocks
@memoryCapacity	the memory cell and bank, plus the world cell for a world processor
@displayWidth, @displayHeight	displays
@totalLiquids	on a factory only its output liquid, on a pump only what it pumps

The full list, property by property, is in the property table: each one says who it is read on and what it gives. That table is taken from the game’s code rather than assembled by hand, so it can be trusted.

What to do with a null answer

There will be no error: sensor does not complain, it puts down null. The program carries on.

Silent failure

If a check for “ammo is zero” always fires, you are almost certainly asking the wrong block or have the property name wrong. null equals zero in an ordinary comparison, and neither the game nor the editor will tell you.

A number does not always mean “how much”

@controlled answers with a number — 0, 1, 2 or 3 — but that is not a quantity, it is a code: nobody, a processor, a player, command mode.

Zero is there for a reason: anything above zero means “somebody is driving it”. So the most common check is not a walk through the codes but a comparison with zero, and jump handles both “greater” and “not equal” here.

Telling exactly who is needed less often; for that the codes have constant names — @ctrlProcessor, @ctrlPlayer, @ctrlCommand. Those are the same 1, 2 and 3. The codes in full are in the property table.

For units @controlled alone is usually not enough: it says “some processor” but not which one. Its partner is @controller, and each has a blind spot of its own; in detail in the lesson “Who is driving the unit”.

Note

In the course sandbox @heat on reactors is always empty. Turrets and drills, on the contrary, are real: @ammo and @progress here are the same as in the game.

Remember

• There are few common properties: health, coordinates, team, size, contents.
• @ammo, @progress, @heat, @memoryCapacity belong only to their own blocks.
• A type answers about the blueprint, a building about itself; an item asked of a type gives the price.
• What a block does not have arrives as null.

Task

Add another Sensor with the plus and ask duo1 for @ammo. You get zero: the turret on this map stands unloaded, and zero here means “no ammo”, not “wrong question”.

Then ask @ammo of the router: that gives null. That is “the property does not apply to this block” — two similar answers to two completely different questions.