# Attachables

The attachables module provides a couple of classes to facilitate attaching objects to one another in simple cases (so if you don't have any need to attach objects to each other in your game right now you can skip this section and come back to it later). The adv3Lite implementation is both simpler and easier to use than the adv3 Attachable class, but handles a far more restricted range of cases (for the sake of keeping things simple). Also, unlike the adv3 Attachable framework, in adv3Lite attachment is not a symmetrical arrangement, i.e. ATTACH A TO B does not mean the same thing as ATTACH B to A. Moreover in adv3Lite attachment is (mainly) implemented as a many-to-one relationship, that is you can attach many As to one B using commands of the form ATTACH A to B (the exception is the Attachable class described below, which allows a many-to-many attachment relationship).

We can make this clearer by means of a concrete example. Suppose we have a fridge magnet. We can then ATTACH MAGNET TO FRIDGE. The magnet is then considered as attached to the fridge rather then vice versa. Since the fridge is the dominant or larger object in this attachment relationship, it could have several magnets attached to it, for example a round magnet, a square magnet, and a star-shaped magnet. All three magnets could be attached to the fridge in turn with the commands ATTACH ROUND MAGNET TO FRIDGE, ATTACH SQUARE MAGNET TO FRIDGE, and ATTACH STAR MAGNET TO FRIDGE. Either before or after being attached to the fridge the magnets could in their turn have objects attached to them, e.g. ATTACH PAPERCLIP TO ROUND MAGNET and ATTACH DRAWING PIN TO ROUND MAGNET. After all these commands had been issued, the three magnets would be attached to the fridge, while the paperclip and the drawing pin would be attached to the round magnet.

The base class for implementing this type of attachment in adv3Lite in the SimpleAttachable. In order to attach two objects, both must defined as SimpleAttachables (or as a subclass thereof). You should then define the allowableAttachments property on the major item (the one things are to be attached to, such as the fridge in our previous example) with a list of objects that can be attached to it (e.g. [roundMagnet, squareMagnet, starMagnet]). For example, if we had just one magnet we wanted to be able to attach to a fridge we might define:

    + fridge: SimpleAttachable 'fridge; large white; refrigerator door'
        "It's a large, white floor-standing refrigerator. "
        remapIn: SubComponent { isOpenable = true }
        allowableAttachments = [magnet]
        isFixed = true
        isListed = nil
    ;

    ++ magnet: SimpleAttachable 'small magnet; red maple; leaf'
        "It's red and shaped like a maple-leaf. You must have picked it up on your
        last trip to Canada. "
        attachedTo = fridge
    ;

In this example, the magnet starts out attached to the fridge, which is why we define attachedTo = fridge and locate the magnet in the fridge (with the ++ notation; note also that to make sure the magnet is on the outside of the fridge we define the interior of the fridge on its remapIn property). If you didn't want the magnet to start out attached to the fridge you'd just locate it wherever you want it to start out and leave its attachedTo property undefined. The above example does, however, illustrate a couple of useful points. First, it shows how you can define an object as starting off attached, and secondly it calls attention to the fact that if you attach one object to another the first object ends up located in the second (which ensures that the first object will move around with the second if the second object is moved), and that when an object is attached to another object the first object's attachedTo property is set to the second object.

More generally, the properties and methods of SimpleAttachable you might commonly want to use are:

- allowableAttachments: a list of items that can be attached to this item (which in general won't be same as the items to which this object can be attached).
- attachedTo: the item (if any) to which this item is currently attached. Normally this is set by the library when the player issues ATTACH and DETACH commands; you only need to set it yourself for objects that start out attached.
- locType: You should treat this as a read-only property. It will be set to Attached when this object is attached to something.
- isFirmAttachment: If this is true (the default) then this object has to be explicitly detached from its parent before it can be moved anywhere else (though the library will carry out an implict DETACH command if the player character takes this object while it is attached).
- allowDetach: If this is true then this object can be detached from its parent with a DETACH command. Otherwise the DETACH command won't work to detach this object (maybe some other command such as UNSCREW would be required, as specified by the game author).
- allowOtherToMoveWhileAttached: If this is true (the default) then our parent object (the one this object is attached to) can be moved while we're attached to it. If it's nil, then the other object cannot be moved while this object is attached to it.
- attachments(): A method that returns the list of objects attached to this object.
- attachTo(other): attaches this object to other under programmatic control.
- detachFrom(other): detaches this object from other under programmatic control; if this object isn't attached to other then the method does nothing.
- isAttachedToMe(obj): returns true if obj is attached to this object (i.e. obj is in the list of attachments) and nil otherwise.
- isAttachedTo(obj): returns true is this object is attached to obj or if obj is attached to this object (i.e., if any attachment relationship exists between the object the method is defined on and obj).

The library defines three subclasses of SimpleAttachable: AttachableComponent, NearbyAttachable and Attachable.

An AttachableComponent is a SimpleAttachable that's treated as a component of the item to which its attached (the handle of a knife, say). An AttachableComponent starts out with its isFirmAttachment property set to true, and its allowDetach property set to nil. It also defines an initiallyAttached property which, if true (the default) means that the Component starts out attached to its immediate container. Moreover, the locType of an attached AttachableComponent is PartOf. If an AttachableComponent starts out as a separate item (e.g. a handle not yet attached to a knife) it effectively becomes a part of (i.e. a component of) the item its attached to when it is attached (e.g. ATTACH HANDLE TO KNIFE would effectively make the handle part of the knife, assuming the handle was an AttachableComponent and the knife a suitably defined SimpleAttachable). Note that if the handle started out attached to the knife and never needed to be reattached to it during the game, there would be no need to make the knife a SimpleAttachable; the knife could then just be a Thing.

A NearbyAttachable is a SimpleAttachable that's moved into the location of the object it's attached to, instead of becoming located within the other object. (This might be useful, say, for connecting lengths of hose or cable together, or assembling a device out of its components). You can override the attachedLocation and detachedLocation properties (on the object to be attached) to tweak this behaviour; for example you could set both to location (meaning the location of the attached object) if you don't want attaching it to the other object to move it at all.

An Attachable is a NearbyAttachable that can be attached to more than one thing at time (as well as having more than one thing attached to it). This is intended for more complex cases than the SimpleAttachable model can handle, such as a cable that's needed to connect a piece of electrical equipment to a power outlet (and so needs to be plugged into both) or a rope used to tie two or more objects together (which needs to be attached to all of them). In addition to the methods and properties it inherits from SimpleAttachable via NearbyAttachable, the Attachable class defines the following:

- attachedToList: the list of items this object is attached to (this should be used in place of the attachedTo property, which just contains a single item). Note that this remains distinct from the attachments property which continues to hold the list of items attached to this one. On an Attachable item the isAttachedTo(obj) method can be used to determine if obj is in either list.
- maxAttachedTo: the maximum number of items to which this object can be attached at once. The default value is 2, on the basis that this is likely to be the most common case. If you don't want there to be any limit at all, you can set this property to nil. Note that the maxAttachedTo property does not impose any limit on the number of items that can be attached to the objects it's defined on (the number of items in the attachments property); it merely limits the maximum length of the attachedToList property.
- reverseConnect(obj): If this method returns true for obj then this reverses the order of connection between self and obj when obj is the direct object of the command; i.e. CONNECT OBJ TO SELF, will be treated as CONNECT SELF TO OBJ. Since the adv3Lite attachment relationship is asymmetric, this method can be used to help enforce the attachment hierarchy intended by the game author.
- multiPluggable: if this property is true (the default) then this allows an Attachable that's also a PlugAttachable to be plugged into more than one thing at a time (e.g. to implement a cable that's needed to make an electrical connection between two different items).

## PlugAttachable

The PlugAttachable class is a mix-in class designed to be used together with either SimpleAttachable or NearbyAttachable. This allows an object to be Plugged into or Unplugged from another object. It's then attached to the other object, but described as being plugged into it. Attaching one PlugAttachable to another is equivalent to plugging it in. For example:

    + plug: PlugAttachable, NearbyAttachable 'electric plug'
    ;

    + socket: PlugAttachable, NearbyAttachable, Fixture 'power socket'
        allowableAttachments = [plug]
    ;

The number of items that can be plugged into something (the socket) at any one time is controlled by the socket's socketCapacity property, which is 1 by default.

If you want to define an object that can be plugged in and unplugged without specifying a particular socket, you can use the PlugAttachable mix-in with an ordinary Thing class and define its needsExplicitSocket property as nil, e.g.:

    + tv: PlugAttachable, Switch, Fixture 'television;;tv'
        "It's currently <<if isOn>>on<<else>>off<<end>>, not that it makes much
        difference to the quality of what appears on the screen. "

        specialDesc = "A TV lurks in one corner of the room. "
        needsExplicitSocket = nil

        dobjFor(SwitchOn)
        {
            check()
            {
                if(!isPluggedIn)
                    "It's not plugged in. ";
            }
        }

        makePlugged(stat)
        {
            inherited(stat);
            if(!stat)
                makeOn(nil);
        }
    ;

adv3Lite Library Manual
Table of Contents | Optional Modules > Attachables
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