MOO WAIF Tutorial

In this example we'll be demonstrating the WAIF type by writing a simple code timer. This will show off several aspects of the WAIF type, including: automatically called verbs (initialization and destruction), instance verbs, instance properties, and a completely contrived example of a class verb.

What is a code timer? It's a very simple tool to help benchmark the time it takes a verb to execute. It's intended to be a one line solution to a problem that would ordinarily take multiple temporary lines of code.

Written by lisdude and last edited 2021-09-01.


First we want a place for our verbs and properties to live. This will be our "class", which is a term that may be familiar to those who know other programming languages.

@create $waif called Code Timing WAIF

For the sake of demonstration, we'll assume our newly created WAIF is #123.


We'll want two properties on our timer: First, the time it was started. Second, the player to report back to:

@prop #123.:start
@prop #123.:player

As you can see, this is ordinary enough. However, each property name is prefixed with a colon. Why is that?

A WAIF can be thought of as two distinct things: The WAIF class and an instantiated WAIF. The WAIF class is a completely ordinary object. It can have normal verbs and normal properties and function like any other object. The instantiated WAIF, however, is special. It exists only within a property or a verb. It's not an object. As such, we need a way to differentiate verbs and properties from the WAIF class vs the WAIF itself, as there are times when you want to be able to call a verb on the instantiated WAIF but not its class, and vice versa. The colon provides that differentiation. We'll see more about the differences between a waif class and an instantiated WAIF later.

At this point, we're done. The WAIF is perfectly usable. If you'd like, you can test it:

@prop me.timer
;me.timer = #123:new()
;me.timer.player = me

Here we instantiated a WAIF using the new() verb (which can be found on the generic WAIF) and stored it in the 'timer' property on your player. You now have access to the start and player properties directly as if they were properties on an object. Fancy! Not all that useful. Notice that the colon is no longer in the property name. This is because the colon is only meant to differentiate between verbs and properties on the class itself. Since this WAIF is instantiated, it has no class verbs or properties and no differentiation is necessary.

Instance Verbs

Now we want our WAIF to actually do something. This is one of the key differences between a WAIF and a LIST: a WAIF can have verbs. For our timer, we're going to define four verbs.

@verb #123::initialize tnt
@prog #123::initialize

this.player = args ? args[1] | player;


This is the initialization verb. When $waif:new() is called, it passes its arguments to the initialize verb on the instantiated WAIF. In this case, it will allow the player to redirect the timer's output to any player it wants. Otherwise, it defaults to the player who called the verb. Please note that no thought has been given to security or input validation in this brief example. That's left as an exercise to the reader.

The first line is the first we'll see of the difference between verbs on a class vs verbs on an instantiated WAIF. this.class is a special property that all WAIF types possess. It returns the object that the WAIF is based on. Its parent, if you will. In this line, we're calling a verb on the parent that doesn't exist on the WAIF instance. Note how, in the Class Verbs and Properties section below, we don't have an extra colon in the increment_lifetime_timers verb.

@verb #123::recycle tnt
@prog #123::recycle



The recycle() verb is another special verb. The server will automatically attempt to call it on an instantiated WAIF when it's time for it to get cleaned up. This gives us an opportunity to stop our timer when the WAIF instance goes out of scope and get the final output before it's lost forever.

@verb #123::stop tnt
@prog #123::stop

total = ftime(1) - this.start;
this.start = 0;
this.player:tell("Total execution time: ", total, " seconds.");


The stop verb will determine the total time the timer has been running, reset it, and display output to the appropriate player. It's setup in this way so that the stop verb can be called manually or automatically when the WAIF is destroyed.

@verb #123::start tnt
@prog #123::start

this.start = ftime(1);


This verb simply sets the start time. You'll notice it's automatically called by initialize() so that the timer is immediately useful, but it can also be called manually if the timer has been stopped.

Class Verbs and Properties

This is where the example gets a little contrived. To demonstrate the difference between class and instance verbs and properties, we need to have some class verbs and properties! So for our example, we'll just keep track of the total number of timer instances that have ever been created. Why not?

Remember that the class is a normal object, so we add and access verbs and properties exactly the same way as we always do:

@verb #123:lifetime_timers tnt
@prog #123:lifetime_timers

return this.total_timers;


Simply return the total number of timers.

@verb #123:increment_lifetime_timers tnt
@prog #123:increment_lifetime_timers

this.total_timers = this.total_timers + 1;


Add one to the number of timers.

@prop #123.total_timers 0


Time to put all of our hard work to the test! To test it, we'll create two simple verbs:

@verb me:timer_test_1 tnt
@prog me:timer_test_1

timer = #123:new();

@verb me:timer_test_2 tnt
@prog me:timer_test_2

timer = #123:new();
"Do exciting things here that we don't want timed.";


Now try them out:

You should see that the timer outputs roughly the same amount of time as the suspend. Now let's try out our class verb:


The output should be 2 if you've only followed the steps above.


Hopefully that gives you a better idea of how the WAIF type works. Now's the time to experiment and get a better feel for it. What happens if you try to call lifetime_timers() on an instantiated WAIF? What happens if you try to call #123:start() or even #123::start()?


Q: Should WAIF always be all caps? Is it an acronym?
A: While I'm not an authority on such matters, here's my take: Conventionally, all type names are all caps. LIST, INT, FLOAT, etc. For this reason, WAIF should always be capitalized. However, you do what makes you comfortable.

Q: How do I recycle a WAIF?
A: Unlike ordinary objects, a WAIF is not recycled. A WAIF only exists as long as some real object holds a reference to it. That means a WAIF must exist inside a property or a running verb for it to exist at all. To 'recycle' a WAIF, simply remove it from every property or running verb and the server will wash it away.

Q: What's with the colons? I still don't get it.
A: With ordinary objects, a child will inherit verbs and properties from its parent. Now imagine that you want the parent to hold one set of verbs and properties and the child to hold an entirely different set. This is what happens with WAIFs. When a colon is present in a verb or property name on a parent class, it means "this verb or property is all the WAIF gets to inherit. Nothing else."

Q: What do you mean when you keep saying instantiated and instance?
A: Instantiating just means creating. You're creating a new instance of the WAIF class. So for example, if you call me.waif = someWaif:new(); then you've just instantiated someWaif and have an instance stored in me.waif.