I understand that in P it's generally said to be a bad idea to use
'global' variables outside the normal object-oriented methodology
but can anyone please advise me on the best way to make a very small
array of integers available to my entire application? I have a main
controller object that had this:
@public
int myIntArray[10];
But despite the public command, I can't seem to access it from another
class. I made sure to include the controller's header file where it's
needed.
What's the easiest way to make some integers available to the whole application?
Thank you all~
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27 dec 2005, at 11.55, Matt Reagan wrote:

I understand that in P it's generally said to be a bad idea to use
'global' variables outside the normal object-oriented methodology
but can anyone please advise me on the best way to make a very small
array of integers available to my entire application? I have a main
controller object that had this:

@public
int myIntArray[10];

But despite the public command, I can't seem to access it from another
class. I made sure to include the controller's header file where it's
needed.

What's the easiest way to make some integers available to the whole
application?

Easiest or best?

In P you have objects, not free floating data. holds data,
and methods that acts on their data. So, who is the "owner" of your
int array? You can probably build a class to hold that data, in which
case you would allow access to that data via methods on that class:

@class MyIntArray : NS
{
@private

int myIntArray[10];
}
- (int) intAtIndex:(int) index;
- (void) setInt:(int) integer atIndex:(int) index

@end

You might want to consider implementing this class as a singleton class.

j o a r

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I actually tried doing that- encompassing the data inside its own
object. But the problem I'm having involves how to get the data when I
need it.

I have a controller object that does much of the processing and
coordinating for the program, its much of the 'guts' of the simple
program, and it is also responsible for init'ing the single instance
of this data object.

That's fine and dandy- the controller can then access the integers via
the data object's accessor methods. The problem is that I have a
custom NSView (among other things) that needs to also access this
data. Since the controller creates the instance of the data object,
it's the only object that has a reference pointing to the data object,
so any other classes doesn't know how to find the data object to
request the integers. I suppose I could create a method in the
controller that would allow me to do this:

int x;
x = [[myController ] giveMeTheXInteger];

But this roundabout way of referencing the controller, which
references the data object, which then returns its integer, seems
really silly it's just an integer. I just need multiple classes to
be able to modify and access it.

Maybe I'm just not understanding how this works, I apologize, I'm a
newbie. I'm not fully understanding how all these objects are supposed
to find each other. C seems like an efficient language, I
can't believe I would have to create an instance variable in every
single class just to point to this data object will I? Thank you
for your feedback, any additional help in explaining this will be
greatly appreciated.
-matt

12/27/05, j o a r <joar (AT) joar (DOT) comwrote:

27 dec 2005, at 11.55, Matt Reagan wrote:

I understand that in P it's generally said to be a bad idea to use
'global' variables outside the normal object-oriented methodology
but can anyone please advise me on the best way to make a very small
array of integers available to my entire application? I have a main
controller object that had this:

@public
int myIntArray[10];

But despite the public command, I can't seem to access it from another
class. I made sure to include the controller's header file where it's
needed.

What's the easiest way to make some integers available to the whole
application?

Easiest or best?

In P you have objects, not free floating data. holds data,
and methods that acts on their data. So, who is the "owner" of your
int array? You can probably build a class to hold that data, in which
case you would allow access to that data via methods on that class:

@class MyIntArray : NS
{
@private

int myIntArray[10];
}

- (int) intAtIndex:(int) index;
- (void) setInt:(int) integer atIndex:(int) index

@end

You might want to consider implementing this class as a singleton class.

j o a r
>
>
>
>
>

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27 dec 2005, at 12.42, Matt Reagan wrote:

But this roundabout way of referencing the controller, which
references the data object, which then returns its integer, seems
really silly it's just an integer. I just need multiple classes to
be able to modify and access it.

I don't think it's silly at all - data hiding is at the core of P,
and object graphs and object relationships are part of this.

That said, there are times when you want to provide public access to
some methods / objects, and that's why I mentioned the singleton
pattern in my original reply. You should read up on it, there's
documentation on that design pattern in Apple's documentation, in the
list archives and most Cocoa / C books you could find. It relies
on using a class method to access a shared instance - so anyone who
has #imported the header file from that class can reference the
shared instance, and it's methods.

An alternative is of course to simply use class methods and a static
variable, and not bother with the creating the shared instance at
all. Personally I prefer to use singleton classes though, as they
allow you to stick to the regular C design & memory management
patterns - less room for errors that way.

j o a r

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I noticed that the responses thus far have neglected to answer the
"easy" part of your question.

If you want to take the "quick and dirty" route for this, it has
nothing to do with C or P. Just use a global variable in
your main controller's source file, as you would in any conventional
C setting:

int myArray[10];

Then make an extern reference to it in the associated header file:

extern int myArray[10];

Now everybody who imports the header file has access to the array.

Daniel

Dec 27, 2005, at 5:55 AM, Matt Reagan wrote:

int myIntArray[10];

But despite the public command, I can't seem to access it from another
class. I made sure to include the controller's header file where it's
needed.

What's the easiest way to make some integers available to the whole
application?

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Thanks everyone for the help!
-matt

12/27/05, Daniel Jalkut <jalkut (AT) red-sweater (DOT) comwrote:
I noticed that the responses thus far have neglected to answer the "easy"
part of your question.

If you want to take the "quick and dirty" route for this, it has nothing to
do with C or P. Just use a global variable in your main
controller's source file, as you would in any conventional C setting:

int myArray[10];

Then make an extern reference to it in the associated header file:

extern int myArray[10];

Now everybody who imports the header file has access to the array.

Daniel
--
Dec 27, 2005, at 5:55 AM, Matt Reagan wrote:
--
int myIntArray[10];
>
>
>
>
But despite the public command, I can't seem to access it from another

class. I made sure to include the controller's header file where it's

needed.
>
>
>
>
What's the easiest way to make some integers available to the whole
application?
>
>
>
>

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Am 27.12.2005 um 15:50 schrieb Daniel Jalkut:
If you want to take the "quick and dirty" route for this, it has
nothing to do with C or P. Just use a global variable
in your main controller's source file, as you would in any
conventional C setting:

int myArray[10];

Then make an extern reference to it in the associated header file:

extern int myArray[10];

Now everybody who imports the header file has access to the array.

Just do yourself and your friends a favor and name the variable
gMyArray or follow some other standard that makes clear this is a
global.

I'd personally would combine two suggestions made: Declare the global
as a static in your source file and write class-level accessor
methods for it through which all others will go. That way, when you
change the size of the array or whatever, you can easily change
central code in the accessor and track down bugs more easily as they
all go through the accessors. I.e.:

#define MY_ARRAY_SIZE10

static int sMyArray[MY_ARRAY_SIZE];

@implementation ArrayWrapperClass

+(int)getIntAtIndex: (unsigned)idx
{
if( idx >= MY_ARRAY_SIZE || idx < 0 )
[NSException raise ];
return sMyArray[idx];
}

+(void)setInt: (int)val AtIndex: (unsigned)idx
{
if( idx >= MY_ARRAY_SIZE || idx < 0 )
[NSException raise ];
sMyArray[idx] = val;
}

@end

Cheers,
-- M. Uli Kusterer
http://www.zathras.de

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