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§10.5. Volume, Height, Weight

What should fit into what? Inform has basically three sizes: small, person-sized, and room-sized. The difference between "small" and "person-sized" doesn't appear much, but it's the difference between an ordinary container and an enterable container; the fact that a person cannot get inside an ordinary container is one of the few size-related rules built into Inform. It will not object to, say, a fishing rod being put inside a matchbox.

Inform does have one built-in measure of the size of a container: its "carrying capacity". This is a maximum number of contents:

The carrying capacity of the rucksack is 3.

This of course allows three anvils, while forbidding four postage stamps. To do better, we need units of measurement, and Dimensions demonstrates setting these up. The Speed of Thought, meanwhile, ventures into the area of unit conversion: having multiple types of unit and being able to express them to the player, or parse these in the player's input.

To be fully realistic in what will fit into what, we need sophisticated three-dimensional models of shapes, both of the items being carried and of the free space remaining inside containers. Depth elegantly simplifies this by approximating items as cuboids, with a given width, length and height: these multiply to give a volume. To fit in a container, a new item's volume must not exceed the volume remaining inside the container, and in addition its three dimensions must also fit in one of the possible arrangements at right angles to the sides. (So this system would indeed prevent a 1x1x100 fishing rod from being put inside a 5x2x1 matchbox, but would also prevent a 12x1x1 pencil from being put into a 10x10x1 box, because it would need to be turned diagonally to fit.)

Lead Cuts Paper provides a different constraint: here we do not let light-weight containers hold heavy objects.

Weight comes in a different way into Swerve left? Swerve right? Or think about it and die?, which exploits up/down map connections to work out which way gravity would take a rolling marble.

* See Liquids for containers with liquid capacity

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*ExampleSwerve left? Swerve right? Or think about it and die?
Building a marble chute track in which a dropped marble will automatically roll downhill.

Receptacles that calculate internal volume and the amount of room available, and cannot be overfilled.

This example draws together the previous snippets into a working implementation of the weighbridge.

**ExampleThe Speed of Thought
Describing scientifically-measured objects in units more familiar to the casual audience.

***ExampleLead Cuts Paper
To give every container a breaking strain, that is, a maximum weight of contents which it can bear - so that to put the lead pig into a paper bag invites disaster.