On Mon, Jun 23, 2003 at 10:04:22PM +0200 Hamish Whittal wrote:
> I have this scenario:
> I have a 'main' program that needs to call on progA under condtions A,
> progB under conditions B, etc.
>
> Now, I would like the progA, progB, progC to remain independent of the
> 'main' program at all times. The only thing I would like to connect them
> is the paramteres....
> Yes, I know this sounds like the place to use Modules and Packages,
> however, I don't think a module can have a 'main' program of it's own.
> The reasons for keeping this independence is to keep the whole system
> portable and modular. At runtime, the users may choose to leave out
> progC and hence the program will not even load this 'program' or set of
> programs....
>
> Can this be done?
>
> I am not sure I am explaining this correctly, so if not, I will try
> again.
I think you will have to explain a little more. Why is it important that
each of your parts needs to have a 'main' program? From your description
it still sounds as though a module would be a good idea. Take these two
modules:
# modA.pm
package modA;
use strict;
use base qw(Exporter);
@modA::EXPORT = qw(main);
sub main {
my $parms = @_;
...
}
1;
# modB.pm
package modB;
use strict;
use base qw(Exporter);
@modA::EXPORT = qw(main);
sub main {
my $parm = @_;
...
}
1;
And in your main program you use require() to pull in either of the two:
# main.pl
...
if ($conditionA) {
require modA;
modA->import;
main("foo");
}
if ($conditionB) {
require modB;
modB->import;
main("bar");
}
Using require() instead of use() has two implications: The first being
that it happens at run-time. Had you used use(), both modules would have
been loaded. In the above case this would have been a problem because
both modules have and export a main() function.
Secondly, require() wont automatically trigger the exporting of symbols
from a module so you have to do that manually. This is done with
PACKAGE->import. The import() method is inherited by your modules from
the Exporter module. It exports everything that is in @PACKAGE::EXPORT
to the caller (which is main.pl in this case).
Tassilo
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