# The Actor Object

## Thing-like Properties

The first and one absolutely essential step in defining an actor (or Non-Player Character, NPC) is to define an Actor object to represent that NPC in the game world. If you're defining an NPC of any complexity, one that involves a number of ActorStates, AgendaItems and TopicEntries, for example, you might wish to place all the code and objects relating to that NPC in a separate source file, rather than in the source file containing the game map, say. If you're defining a really simple NPC for which the Actor object alone will suffice, you probably do't need to do this.

The Actor class inherits from Thing, and you can thus define/override/use all the usual properties and methods of Thing on Actor, if you so wish/need. If, however, you plan to use ActorStates (which you don't have to) it makes better sense to define the corresponding properties on the ActorState (from which the Actor object will then obtain the appropriate value).

The common properties you will normally want to define on all Actors, in just the same way as you'd define them on Thing are:

- vocab: defining this effectively defines the name at the same time
- desc: the basic (non state-specific) description of the Actor
- location: the starting location of the Actor (if you're defining the Actor in a separate source file it may be useful to do this via the @ part of the template).
- isHim/isHer/isGenderNeutal: if the Actor is a human-like person you'll want to define either isHim = true or isHer = true or isGenderNeutral = true to define the Actor's gender (and thus the pronouns that can be used to refer to him, her or them); note that this property can also be set via the vocab property.
- globalParamName: this can be particularly useful on Actors whose names change during the course of the game (e.g. from 'the tall man' to 'George'), since the globalParamName can be used in message parameter strings like '{The subj george} {is} here' to produce the right form of the name at any time in the game. Note that the library defines this for you, using the object name (e.g. giving an actor object called george the globalParamName 'george') unless you define your own globalParamName for the actor. It will normally be most convenient to accept the library default.
- isFixed: by default this is true for an Actor, on the assumption that most actors can't be picked up and carried around; if you want a portable Actor in your game you would need to override this property to nil.

A minimal Actor definition might thus look something like this:

    george: Actor 'George; tall thin; man; him' @hall
        "He's a tall thin man. "

        globalParamName = 'george'
    ;

We might additionally define the following properties of an Actor if we're not going to use any ActorStates with this Actor; otherwise one would define them appropriately on the ActorState objects:

- specialDesc: this normally does need to be defined either on the Actor or on its ActorStates to provide a paragraph about the Actor in room description listings (e.g. "George is standing a short way across the room"). The default behaviour is for Actor.specialDesc to use the specialDesc property of the current ActorState, so you'd only override specialDesc on the Actor either if you weren't planning to use any ActorStates with the Actor or you wanted the specialDesc to remain the same regardless of ActorState.
- stateDesc: this is a state-specific description added to what is displayed from the desc property when the Actor is examined. The default behaviour is for Actor.stateDesc to return the stateDesc of the current ActorState, but you can override it on the Actor if you're not using ActorStates with that particular Actor.
- beforeAction(): by default this defers to the beforeAction method of the current ActorState, but it also calls actorBeforeAction(), which you can use for before notications that are state-independent.
- afterAction(): by default this defers to the afterAction method of the current ActorState, but it also calls actorAfterAction(), which you can use for after notications that are state-independent.
- beforeTravel(traveler, connector): by default this defers to the beforeTravel() method of the current ActorState, but it also calls actorBeforeTravel(traveler, connector), which you can use for before travel notications that are state-independent. Note that the beforeTravel() method of Actor also checks whether the travel might end a conversation; it's probably best not to override it even if you aren't using ActorStates and to use actorBeforeTravel() instead.
- afterTravel(traveler, connector): by default this defers to the afterTravel() method of the current ActorState, but it also calls actorAfterTravel(traveler, connector), which you can use for after travel notifications that are state-independent.
- remoteSpecialDesc(pov) (only relevant if you're using the SenseRegion module). This is used instead of the specialDesc if the actor is being viewed from a remote location. If the actor has a current ActorState then by default we use the ActorState's remoteSpecialDesc(), otherwise we use the Actor's actorRemoteSpecialDesc(), which by default simply reports the presence of the actor in the remote location.

## Actor-Specific Properties

In addition to the properties the Actor class more or less shares with Thing are a number peculiar to Actor. The most commonly useful of these (from the point of view of the ones game authors might use) are:

- curState: the Actor's current ActorState. Note, while it is legal for this to be nil (in adv3Lite), it should normally be nil only on Actors that don't use ActorStates at all.
- setCurState(stat): set this Actor's current ActorState to stat. This method should always be used to change the ActorState; don't change the value of curState directly.
- startFollowing(): call this method to make this Actor start following the player character around.
- stopFollowing(): call this method to make this Actor stop following the player character around.
- sayFollowing(oldLoc): displays a message when this Actor follows the player character into a new location from oldLoc. By default we either call the sayFollowing() method of the current ActorState (if there is one) or the actorSayFollowing(oldLoc) method on the Actor if the Actor's curState is nil. In either case the default message produced by the library is of the form "George follows behind you."
- arrivingTurn(): this method is executed on the Actor immediately after the sayFollowing() message is displayed to allow the Actor to carry out additional handling on following the player character to a new location. By default Actor.arrivingTurn() calls arrivingTurn() on the current ActorState if there is one or actorArrivingTurn() if curState is nil.
- allowOtherActorToTake(obj): returns true if another actor (including the player character) is allowed to take obj while obj is in this Actor's inventory; by default this method simply returns nil.
- canCatchThrown(obj): returns true (the default) if this actor can catch obj when obj is thrown to the actor. If this method returns nil, obj falls into the actor's location instead.
- travelVia(conn, announceArrival = true): make this actor travel via the connector conn and display a message reporting the movement if it's visible to the player character. If the optional second parameter is nil the sayArriving() message will be suppressed.
- scriptedTravelTo(dest, exec?): send this actor on a path to dest (if dest is supplied as a Room or Thing) or along a user-defined path (if dest is supplied as a list of TravelConnectors). For a full explanation of how to use this method, see the article on NPC Travel in the TADS 3 Technical Manual.
- sayDeparting(conn): the message to display when the player character sees this actor departing (via a call to travelVia(conn)). By default we use the current ActorState's sayDeparting() method or, if there is no current ActorState, our own sayActorDeparting(conn) method.
- sayArriving(fromLoc): the message to display when the player character sees this actor arriving (via a call to travelVia(conn)). By default we use the current ActorState's sayArriving() method or, if there is no current ActorState, our own sayActorArriving(fromLoc) method. The fromLoc parameter is the location from which the arriving actor has just arrived.
- pcArrivalTurn: The last turn (if any) on which the player character arrived in the location of this actor. This is mainly for use by pcJustArrived.
- pcJustArrived: flag, this is true if the player character arrived in the location of this actor on the current turn and nil otherwise. This can be used, for example, to adjust our specialDesc to reflect the player character's arrival on the scene.

There are also a number of properties and methods specific to actor conversation:

- lastConvTime: the turn on which the player character last conversed with this Actor.
- conversedThisTurn: true if the player character conversed with this Actor on this turn, nil otherwise.
- conversedLastTurn: true if the player character last conversed with this Actor on the previous turn, nil otherwise.
- canEndConversation(reason): returns true if the Actor can end the current conversation for reason. By default we return canEndConversation(reason) on the current ActorState if there is one, or actorCanEndConversation(reason) if curState is nil. reason can be one of:
  - endConvBye: the player character says goodbye to the Actor.
  - endConvLeave: the player character departs to a new location in the middle of the conversation.
  - endConvBoredom: the Actor becomes bored with waiting for the player character to speak.
  - endConvActor: the Actor wishes to terminate the conversation for some other reason.
- endConversation(reason): make the Actor terminate the current conversation with the player character, provided canEndConversation(reason) will permit it. Normally game code would only call this with reason = endConvActor; the other reasons come about indirectly as the effect of other occurrences.
- attentionSpan: the number of turns this Actor will wait for the player character to speak (once a conversation is underway) before becoming bored with waiting and terminating the conversation. If this is nil (the default) this Actor never becomes bored.
- canTalkTo(other): can this Actor talk to other? By default this returns true if the Actor can hear other.
- informedAbout(tag): has this Actor been informed about the information denoted by tag (where tag is a single-quoted string value like 'fred-burgled' or 'martha-affair' or 'find-orb')?
- actorSay(txt): have the actor say something (and/or the player character say something to the actor), thereby making the actor the current interlocutor. Note, this is not the normal way to handle conversation, but is provided for use as a short-cut in certain kinds of circumstances. See further under NPC-Initiated Conversation.

The purpose of some of the above should become more apparent when we get deeper into the conversation system. There are also a number of methods used for manipulated the Actor's agenda, whioh will be explained in the section on AgendaItems. Most of the other methods and properties of Actor are intended for internal use by the library, and would not normally be directly employed in game code.

## Attacking, Touching and Kissing

The way Actor (and to some extent Thing) handles responses to ATTACK, TOUCH and KISS is slightly unusual. This is because while attacking, touching or kissing someone is not exactly the same as conversing with them, it is nevertheless a potentially complex form of interpersonal behaviour.

All three actions can be ruled out at the verify stage (on Thing or Actor) by setting isAttackable, isFeelable or isKissable respectively to nil. By default these are all true, except for isAttackable on Thing (on the basis that it doesn't normally make much sense to go around attacking inanimate objects).

All three actions can also be ruled out at the check stage (on both Thing and Actor) by setting checkAttackMsg, checkFeelMsg or checkKissMsg to some non-nil value (normally a single-quoted string, although a double-quoted string or a method that displays some text will also work). This will cause the action to be stopped at the check stage with a display of the message defined on the relevant property. The default value of all three properties is nil.

At the action stage, all three commands work differently on Actor from the way they do on Thing (since attacking, kissing or touching an inanimate object is rather different from attacking, kissing or touching a person). On the Thing class the result is to display the futileToAttackMsg (if attacking is allowed at all, by default it isn't since it's stopped at the verify stage so we'd normally see the cannotAttackMsg instead), the feelDesc, or the futileToKissMsg if it is non-nil (by default it's nil) or else the default message generated at the report stage, respectively.

On the Actor class, however, if any of these commands reach the action stage they are handled quite differently, on the grounds that a person will react very differently to being attacked, touched or kissed than an inanimate object. In the first instance, the ATTACK, TOUCH or KISS command will be handled by a HitTopic, TouchTopic or KissTopic if one is available; otherwise the attackResponseMsg, touchResponseMsg or kissResponseMsg (all of which should be defined as single-quoted strings) is displayed.

At first sight it may seem a bit confusing that some properties refer to 'feel' (e.g. feelDesc, checkFeelMsg) while others refer to 'touch' (e.g. touchResponseMsg). The pattern is that properties defined on Thing use 'feel' while those peculiar to Actor use 'touch'; the rationale of this is that the naming of the Thing properties follows the convention of using the action name, which is actually Feel, but that it's rather more natural to talk in terms of touching someone than feeling someone (hence touchResponseMsg and TouchTopic). However, to alleviate any confusion that might arise the library defines a number of macros that convert the plausible but wrong form of the property name into the correct one:

- checkTouchMsg into checkFeelMsg
- feelResponseMsg into touchResponseMsg
- isTouchable into isFeelable
- cannotTouchMsg into cannotFeelMsg
- touchDesc into feelDesc
- checkHitMsg into checkAttackMsg
- hitResponseMsg attackResponseMsg

While these can't be relied upon in every single case, and it's better to use the correct names, these macros will probably cover the great majority of cases where the plausibly wrong property name is used, so that most of the time it won't matter whether, for instance, you use feelResponseMsg or touchResponseMsg as the property name, since in most common cases they'll end up meaning exactly the same thing.

## ProxyActor

Defining an actor is not just a matter of defining a single Actor object, but also a number of other objects, such as ActorStates, TopicEntries, AgendaItems, and ConvNodes that define the actor's behaviour. For a very complex actor we may find that we have so many of these that we'd ideally like to split them over more than one file. The apparent difficulty is that all (or most) of these objects need to be directly located directly within the Actor whose behaviour they help to define. We could explicitly set the location property of all such objects to refer to an Actor object in another file, but this could soon become quite laborious, and may easily lead to errors if we slip back into using the + notation we're more used to. To address these problems we can use a ProxyActor object. This can be placed at the head of any second or subsequent file we're using to define the same actor, and then we can continue to use the + notation to locate ActorStates, AgendaItems and all the rest in the ProxyActor just as it if were the original Actor. The only other step we need to take is to set the ProxyActor's location property to the Actor it's standing in for, which we can do via the @ notation in the ProxyActor template, e.g.:

    ProxyActor @guard
    ;

    + guardAlertState: ActorState
       isInitState = true
       specialDesc = "A burly guard blocks your path, eyeing you suspiciously. "
       stateDesc = 'You certainly don\'t want to mess with him. '

       beforeTravel(traveler, connector)
       {
          if(traveler == gPlayerChar && connector == forbiddenDoor)
          {
              "The guard blocks your path with a warning snarl. ";
              exit;
          }
       }
    ;

    + guardAgenda: AgendaItem
       ...

    ;

adv3Lite Library Manual
Table of Contents | Actors > The Actor Object
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