Re: Procedure pointers - can I do this??

[Simon Coulter <shc@xxxxxxxxxxxxxxxxx>]

On 18/12/2004, at 7:05 AM, Larry wrote:

> That's an interesting idea. I'd find it scary if it worked. 
> Personally, I'd
> rather use getter methods to retrieve variable data across module
> boundaries. My reasoning is that, as RPG only really has two access
> modifiers - PUBLIC (exported) and PRIVATE (not exported), you can't 
> have
> "package" or "protected" access to your own data. Thus, if you export a
> variable from one of your modules you are allowing it to be modified 
> by ANY
> client program that binds to your service program.

Not true. You can't get protected semantics but you can simulate 
package behaviour.

Specifying EXPORT will always export the variable or procedure from the 
module but it is only available to other modules that directly bind to 
it. If the module containing EXPORT is bound into a service program 
then EXPORT means it is a candidate for export. Whether it is visible 
by consumers of the service program depends on the the setting of 
EXPORT on CRTSRVPGM. If you use EXPORT(*ALL)--really dumb for reasons 
explained in the archives--then any candidate export will be visible. 
If you use binding source then you can omit the candidate variable or 
function from the public interface. It will still be available to other 
modules bound directly into the service program but will not be 
accessible by consumers of the service program.

> You may want some of your
> own programs access to the data, but not ANY program. The only safe 
> way to
> allow "restricted" access is to encapsulate the data through 
> sub-procs. The
> sub-proc can then perform some form of validation prior to returning 
> the
> variable data. The other beauty of encapsulation is that you can 
> modify HOW
> you generate the data internally, and return different values in 
> different
> scenarios. By laying bare your internal variables you restrict your 
> ability
> to re-design your module code.

Notwithstanding my comments above I agree that providing so-called 
accessor methods is the best approach.

Regards,
Simon Coulter.
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