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Object Inheritance

Note: a lot of this is new to Phantasmal 0.016. If you're still using a previous version, allow me to recommend the old inheritance tutorial rather than this one.

One way to potentially save yourself some time, when building objects that have some relationship to each other, is to build a parent object for some or all of them. If you're building a large number of sun-drenched rooms in an outdoor labyrinth then lots of them are likely to have grass, sunlight, a hedge, a view of a tower and so on. You can put all those various details into a single parent object and make your tens or hundreds of labyrinth rooms all implement them automatically. This tutorial can show you how.

As a time-saver, inheritance is primarily a way to inherit object details. That's a useful thing, but it doesn't do everything. Object nouns and adjectives will also be inheritable as of Phantasmal 0.016. Things like weights and heights already are. We're considering inheriting object descriptions, but it's not entirely clear how the commands for that should work.

So, back to that sun-drenched labyrinth. You're going to need a parent room, which should be clearly marked as such and not connected (via exits) to any other room anywhere. That keeps people from randomly walking into it and changing stuff. So use @make_room to make the parent room. Your parent rooms are allowed to have their own parents, but in this example there's probably no reason to bother. Take note of the parent room's object number when @make_room tells you what it is.

For your brief and glance descriptions you should put something like "labyrinth parent room", and for your look description you should put something like "this room contains details for other labyrinth rooms. You should never, never be able to enter it." You shouldn't add any exits to or from it. Remember that if anybody ever changes something here it will be propagated to all your child rooms, so only change the parent room if you actually mean to.

You'll also want an ordinary labyrinth test room to try out the nifty inheritance tricks. Go ahead and create one with @make_room. Up to this point, when @make_room asks you for a parent object, you've probably just been hitting enter to leave it blank. And that's been the right thing to do. But when you make the labyrinth test room, you should instead type the number of the labyrinth parent room -- the one we told you to take note of awhile back. You wrote it down when @make_room told it to you, right?

The description can be whatever you like, but for the full example experience, I recommend mentioning sunshine and a distant tower in the description. That way people can look at them.

Now, go ahead and make a new detail with @make_detail. Make it a part of the labyrinth parent room, not the labyrinth test room. Describe the sunshine playing on the grass and hedges, and how you can see the dust motes swirling in it. Give the sunshine nouns like sun, sunshine, dust and motes, and adjectives like bright, shiny and dust. That's so that you can look at the dust motes, the shiny motes or the sunshine and get the same description back.

To test it out, go to the labyrinth parent room and look at the dust motes. Now go back to the labyrinth test room and do the same. If you want, go ahead and add more details to the labyrinth parent room for things like grass, the tower, the hedges and the other stuff you can see. If you were a Skotos builder doing a Castle Marrach room you'd be spending two or three hours at least on all the descriptions, so don't be shy about taking ten or fifteen minutes on this. Your best role-players will eat this stuff up. And remember, every minute you spend on the details in the parent room is that much more detail in every child room. That's how inheritance in Phantasmal saves you time!

So test it out. Make another child room. That's another room like the labyrinth test room, one that also inherits from the labyrinth parent room (whose number you still remember, yeah?). After making this fresh-minted room with @make_room and giving it the labyrinth parent room as a parent, go ahead and look around at the grass, the dust motes, and everything else you made details for. And there they are!

Note how just by making a room with a cool parent, you've suddenly gotten a lot of details for free. This is inheritance, but it's not the kind you're used to in an Object Oriented programming language (just in case you're a programmer). That kind of inheritance is also called code inheritance because it's code being inherited. Those languages almost never allow data inheritance, which is what you're seeing here in Phantasmal. That's because these details are object data, not methods or any other kind of code. MUDs tend to be better served by data inheritance, at least for "physical" objects in the MUD world.

What if you want to make a room that's a little different? Let's say you want a cool, shady labyrinth room in one specific place, but you'd like the grass, the view of the tower and so on to stay the same. Make a new room and call it "shady labyrinth room". Describe it appropriately. But make sure that its parent is still the same labyrinth parent. So to start out with, it looks just like the other sunny labyrinth rooms. How do you change it?

First, add a detail to the new shady room. You might give it nouns like 'hedge', 'shade' and 'shadow', and adjectives like 'shady' and 'cool'. Then when a player looks at the cool shadow or the shady hedge, he'll see the new shady version. Check out your new room with the @stat command -- you should see a detail list with the new detail, and also a detail list with the full set of details from the parent as well.

But you'd like to get rid of the sunshine and dust motes above, since they shouldn't be here, or shouldn't look the same. To do that, remove the detail from the child object. That's right: remove the parent's detail from the child object. Each child object keeps a list of parent details that it overrides -- details that the parent has, but the child does not. By removing the parent's detail, you add the removed detail to that internal list. Doublecheck with @stat. The parent detail for sunshine and dust motes should be gone.

Multiple Inheritance

An object can have more than one parent. Some attributes like weight, height, weight_capacity and so on are inherited entirely from the first parent. Other attributes like nouns and details are combined from all parents. If you wanted to make certain labyrinth rooms shady and other sunny, and make certain rooms large and others small, you could make large and small parent rooms, and shady and sunny parent rooms, then inherit from either large or small and either shady or sunny to combine them. The volume capacity of the room (and thus, how many players may be inside it at once) is set from the first parent, which would be either large or small. However, the details are from all parents, so the room would also inherit the shady or sunny detail objects from the shady or sunny rooms. Additional parent objects that add extra details, nouns, adjectives, etc are called mixin objects, or mixin parents because the mix additional details in without interacting directly with the other parent classes.

Usually it's easier to inherit another room from a parent object before having the child inherit it than to make mixin objects. For instance, if all rooms were the same size but you had both shady and sunny rooms, then you could make a "labyrinth room" parent, and then inherit shady and sunny children from it. However, if you have multiple attributes that vary independently, you may find a mixin parent is easiest. For instance, you could have shady, small rooms, sunny, large rooms, shady, large rooms or sunny, small rooms in the above, so it made sense. If every small room is also shady and every large room is also sunny, you're probably better off avoiding multiple inheritance -- it can be complicated to use. The single-inheritance solution is easier.

The @set_object_parent command

The only other thing you should know about inheritance is the way to change or remove object parents. The @set_obj_parent command is your friend here (check its online help!). You can set an object #1124's parent to object #375 by saying "@set_obj_parent #1124 set #375". You can then make it parentless again by saying "@set_obj_parent #1124 none". You can set multiple parents by saying "@set_obj_par #1124 add #391 #241", or "@set_obj_par #1124 set #375 #391 #241". Note that the order of the parents matters, and that added parents are appended to the end of the list.

Note that parents are also called Archetypes, and that Skotos calls them ur-objects. Phantasmal uses the internal name 'archetype', but tends to call them parents in the help and tutorials because people find the word less imposing.

Now go build some more stuff by following the tutorials.