Re: [Swarm-Support] Questions about passing SwarmObjects within other objects

[Paul Johnson]

Hi, Paul:

Here's the answer.

id world;
HeatSpace * world;
id <some_protocol> world;

are all acceptable.  id means a "pointer to an object", so you don't put 
a * there, since the pointer idea is in the heart of it.

The advantage of declaring

HeatSpace * world;

is that the compiler knows exactly where to find methods for the world 
object to use.  It is one way to solve the problem that, if you declare 
a method slightly differently in two classes, the compiler will complain 
to you.  Suppose you have

- (double)getValue;

in the HeatSpace class, and

- (int)getValue;

in another class.  If you used the declaration

id world;

and then

[world getValue];

The compiler will complain that various methods "getValue" were found 
and it will bother you because their signatures are not exactly the same.

On the other hand, with

HeatSpace * world;

it knows exactly which class you are using, so its not confused by the 
difference in method names.

In some Swarm classes, you are wise to include protocol declarations. 
You are not supposed to declare things with class names. I don't recall 
exactly which ones, but if you grab some 4 year old swarm code, you will 
find the problem right away when you try to compile.  It does not want 
you to do things like

ZoomRaster * aRaster;

or was it:

Grid2d * world;

?

Rather, it wants


id <ZoomRaster> aRaster;
id <Grid2d> world;



Paul Thompson wrote:
> I'm Paul Thompson, a graduate student at Rochester Institute of
>
> Below is the oft-perused ObserverSwarm of the heatbugs app.  My
> concern is with the variable declaration for world and HeatSpace. 
> More precisely, why is world declared as a variable while HeatSpace is
> declared as a pointer?



--
Paul E. Johnson                       email: address@hidden
Dept. of Political Science            http://lark.cc.ku.edu/~pauljohn
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