Table of Contents |
Schemes and Devices > Just the
Ticket
Just the Ticket
The description of the Airport game calls for a ticket found by picking up a newspaper in the snack bar. We’ve already implemented the newspaper; now it’s time to implement the ticket:
ticket: Thing 'plane ticket'
"It's a ticket for flight TI 179 to Buenos Aires. "
readDesc = (desc)
specialDesc = "A ticket lies on the ground. "
useSpecialDesc = (location == getOutermostRoom)
;
That was the easy bit. The only new thing here is the use of the
useSpecialDesc property to determine when the specialDesc is used. We
want “A ticket lies on the ground” to appear in the room description
whenever the ticket is notionally lying on the ground, which is whenever
it’s directly in a room rather than some other object; we can test this
by testing whether its location is the same as the room it’s in, as
above. While we’re at it we define readDesc as
(desc) so that READ TICKET gives the same
response as X TICKET. The next trick is to hide it in the newspaper so
that the player character finds it if he either searches the newspaper
or picks it up.
It would be rather complicated to make the newspaper a container just so we can hide the ticket in it. Fortunately we don’t need to; instead we can make use of the hiddenIn property. This contains a list of items that are notionally hidden inside an object, and are discovered when the player issues a LOOK IN or SEARCH command. To use hiddenIn we list the items we want the player to be able to discover in this way, while defining the items elsewhere in our code with no starting location (i.e. a starting location of nil), as with the ticket above. We can thus put the ticket in the hiddenIn property of the newspaper:
++ newspaper: Thing 'newspaper; narcosia; paper herald'
"It's a copy of the latest edition of the <i>Narcosia Herald</i>. "
readDesc = "A quick skim of the paper reveals nothing unusual for this part
of the world. Yet another government minister is denying charges of
...
to this godforsaken hell-hole. "
hiddenIn = [ticket]
;
In the same way we could use hiddenUnder or
hiddenBehind to hide items under or behind
another object.
This will work well enough if the player thinks to LOOK IN or SEARCH the
newspaper, but nothing happens if the player character just picks it up.
Picking up an object would reveal any items in its
hiddenUnder or
hiddenBehind lists, on the basis that they
would be left behind when the object is picked up and hence revealed to
view, but if an object is picked up anything hidden in it is assumed to
travel with it. We can change that by overriding the revealOnMove()
method, which defines what happens when the object is moved. By default
this is the method that reveals anything hidden under or behind the
object, but since we’re not hiding anything under or behind the
newspaper we can override this method to do just what we need:
++ newspaper: Thing 'newspaper; narcosia; paper herald'
"It's a copy of the latest edition of the <i>Narcosia Herald</i>. "
readDesc = '''A quick skim of the paper reveals nothing unusual for this part
of the world. Yet another government minister is denying charges of
...
to this godforsaken hell-hole. '''
hiddenIn = [ticket]
revealOnMove()
{
if(hiddenIn.length > 0)
{
"As you pick up the newspaper a ticket falls out of it
and lands on the floor. ";
ticket.moveInto(getOutermostRoom);
hiddenIn = [];
}
}
lookInMsg = (readDesc)
;
We first check that there’s something still hidden in the newspaper
before doing anything else, since we only want the ticket to fall out of
the newspaper the first time it’s picked up, and not thereafter. Then,
if the ticket is still hidden in the newspaper, we display a message to
say that it flutters out and lands on the floor, move the ticket to the
enclosing outer room, and empty the hiddenIn list. Although this version
of revealOnMove() will work perfectly well for
this game, if you wanted a more generalized version of the routine that
worked whatever was hidden in the newspaper you could write:
++ newspaper: Thing 'newspaper; narcosia; paper herald'
"It's a copy of the latest edition of the <i>Narcosia Herald</i>. "
readDesc = '''A quick skim of the paper reveals nothing unusual for this part
of the world. Yet another government minister is denying charges of
...
to this godforsaken hell-hole. '''
hiddenIn = [ticket]
revealOnMove()
{
if(hiddenIn.length > 0)
{
"As you pick up the newspaper <<list of hiddenIn>> {prev} {falls}
out of it and land{s/ed} on the floor. ";
moveHidden(&hiddenIn, getOutermostRoom);
}
}
lookInMsg = (readDesc)
;
Here, \<\<list of hiddenIn\>\> provides a list
of everything that’s hidden in the newspaper, while the
{prev} tag then ensures that the verbs
{falls} and
land{s/ed} will agree with the list, whether
it turns out to be a singular or plural subject (e.g. “a ticket
falls…” or “a ticket and a leaflet fall…”). Meanwhile the
moveHidden(&prop, loc) method moves everything
in the prop list to loc and then sets prop to []. Note that we
pass the property pointer &prop to this method. I repeat, we don’t
actually need this more general form of
revealOnMove() in this game; it’s shown here
so you can see how to do it if you need it in your own game.
One last thing: once the ticket has fallen out of the newspaper then
LOOK IN NEWSPAPER will produce the response “You see nothing of interest
in the newspaper”, which could rather too easily be taken as a comment
on the paper’s contents. To avoid this, it would be better if LOOK IN
NEWSPAPER worked the same as READ NEWSPAPER once there’s nothing left
inside it. When LOOK IN has nothing else to display, it displays the
object’s lookInMsg. So here the easiest thing to do is to define
lookInMsg to be the same as
readDesc. But then we hit another apparent
snag: lookInMsg would normally be defined as a
single-quoted string but we defined readDesc
as a double-quoted string. Fortunately, adv3Lite also allows us to
define it as a single-quoted string, so we need to change it to one
here. But our original definition of the newspaper’s
readDesc contained a number of apostrophes
which we’d now need to escape with backslashes. To avoid having to do
this, we use the alternative way of defining a single-quoted string, by
starting and ending it with three single-quote marks in a row ‘'’like
this’’’. This removes the need to escape any apostrophes/single-quote
marks (two names for the same character here) within the string.
(Alternatively, we could have got away with defining
lookInMsg = readDesc, since this is an
instance where adv3Lite allows a double-quoted string to be used in
place of the expected single-quoted one, but this isn’t always the case,
so don’t get into the habit of thinking they’re always interchangeable!)
Now try compiling and running the game again to test that the newspaper
and ticket work as expected. Use whichever version of
revealOnMove() you prefer.
adv3Lite Library Tutorial
Table of Contents |
Schemes and Devices > Just the
Ticket