Re: objective-c question

[Benedikt Stefansson]

Hi,

This is a perfect example of where you should use protocols (which I belive
are similar to templates in C++ although I don't want to go out on a limb on
this). A protocol only defines the interface to methods and nothing else, i.e.
like an interface without the instance variable declaritions. So your
DemandCurve protocol file (DemandCuve.h) would be:

(#imports...)
@protocol DemandCurve

- (double)getQuantity: (double)price;

@end

And your LinearDemandCurve.h file would be:

#import DemandCurve.h

@interface LinearDemandCurve: SwarmObject <DemandCurve> {
    (instance variables...)
}

@end

The LinearDemandCurve.m file would then be:

#import LinearDemandCurve.h

@implementation LinearDemandCurve

- (double)getQuantity: (double)price {
    (some stuff...)
 }

When you create a LinearDemandCurve object, for example in ModelSwarm, you
should cast the type as:

id <DemandCurve> demandFunction;

Now you can even switch demand functions on the fly, the compiler won't
complain because they all adhere to the same protocol.

The best Objective-C book is the one from Apple, look for the link on the
Swarm website or at Apple under their MacOS-X-Server documentation.

Regards,
Benedikt

Tamas Papp wrote:

> I'm writing a model that needs different demand curves (functions which
> assign a quantity demanded to any given price.) I thought of writing a
> "placeholder" class, DemandCurve, and subclasses like LinearDemandCurve,
> PolynomialDemandCurve, etc. I define DemandCurve as
>
> @interface DemandCurve
> {
> }
>
> - (double)getQuantity: (double)price;
> @end
>
> and then writing the subclasses. The classes which use a demand curve
> would get a pointer to a DemandCurve subclass, but use it as a DemandCurve
> because they only need the getQuantity function. How is this done in
> Objective-C? I only have experience with C++.
>
> Regards,
>
> Tamas
>
> P.S.: Does anybody know and URL for a good intoductory & reference page
> for Objective C online?
>
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--
----------------
Benedikt Stefansson                 address@hidden
Department of Economics, UCLA       Fax. (310) 825-9528
Los Angeles, CA 90095-1477          Tel. (310) 825-1777



                  ==================================
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