| Chapter 4: Kinds |

| 4.7. New value properties

Moving on to properties which contain values, such as the "matching key" property of a door or a container, we need to use a different formulation.

> A dead end has some text called river sound. The river sound of a dead end is usually "a faint whispering of running water". The Tortuous Alcove has river sound "a gurgle of running water".

The property "river sound" is now applicable only to dead ends, and we would not be allowed to talk about it in any other context. As can be seen, it holds a piece of text. If we tried the following:

> The river sound of the Tortuous Alcove is 7.

...then Inform would object, because the number 7 is the wrong kind of value to go into the "river sound" property. If we need a numerical property, we can try this instead:

> A dead end has a number called the difficulty rating. The Tortuous Alcove has difficulty rating 7.

Suppose that we were to add:

> The Exquisitely Narrow Defile is a dead end.

The Defile must have a river sound, of course, because we said that every dead end would have one. But we haven't specified it. What Inform does is to start off the property holding the "default value" for this kind of value: that is, it sees that the river sound has to be "some text", and it fills in the default value for text: which is the empty text, consisting of no words at all, and written "". Similarly, its difficulty rating is set to 0. (A table of the kinds which can be used for properties, and their default values, can be found in the Kinds index.)

44
| Example Would you...? Adding new properties to objects, and checking for their presence.

45
| Example Straw Boater Using text properties that apply only to some things and are not defined for others.

Sometimes we like to give properties to kinds of thing, but not fill them in in all cases. For instance, we might have vehicles that optionally make noise, and those might have a "movement sound". All properties have a default value, which we can find by looking in the Kinds tab of the index. This is what the property will be set to automatically, if we do not change it ourselves. In the case of a text property, that is ""; so for instance we might use our movement sound thus: "Straw Boater" Boathouse is a room. "A boathouse circa 1915, which -- though in poor repair -- still suggests Sunday afternoon jaunts taken by women in white gowns and men in straw hats." North of the Boathouse is the Shallow Water. The description of Shallow Water is "Just south is the boathouse, and beyond it are trees and the marble terrace of the house above. The water deepens to the north." North of Shallow Water is Deep Water. The description of Deep Water is "From here the boathouse has dwindled invisibly to the south, and you have a broad panorama of the shoreline, all the way down to the Skeleton Point Lighthouse in the southeast." A vehicle has some text called the movement sound. The sailboat and the motorboat are vehicles in the Boathouse. The movement sound of the motorboat is "VRRRROOOMMMM..." Understand "boat" as the sailboat. Understand "boat" as the motorboat. Note that we haven't given the sailboat any movement sound at all. After going somewhere by a vehicle (called cart): if the movement sound of the cart is not "", say "[the movement sound of the cart][paragraph break]"; continue the action. Instead of exiting when the player is in a vehicle and the location is not the Boathouse: say "You're not dressed for a swim." Instead of going somewhere when the player is not in a vehicle: say "You'd rather not try to make this journey by swimming alone." Test me with "n / get in sailboat / n / get out / s / get in motorboat / n / n".

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