Date sent: Mon, 04 Feb 2002 11:27:38 -0800
From: Tarak Parekh <[EMAIL PROTECTED]>
> I was a little confused regarding scopes of packages. I did read
> portions of
> Programming Perl but am still a little unclear.
>
> Basically, I am trying to implement a simple form of RPC in which a
> command takes in a function name and passes it across to a daemon. The
> daemon using symbolic referencing invokes the function.
>
> the daemon sources in 3 libraries (use A; use B; use C;)
> Let's say A contains functions - foo, bar
> and B contains functions - foofoo, barbar
> C contains functions - morefoo, morebar
>
> The daemon's top few lines look like
> ----------
> package daemon;
>
> use strict;
>
> use A;
> use B;
> use C;
>
> A.pm's top few lines look like
> ----------
> package A;
>
> use strict;
>
> use vars qw(@ISA @EXPORT);
You forgot to
require Exporter;
> @ISA = qw (Exporter);
> @EXPORT = qw (foo bar);
>
> sub foo
> {
> print "foo called\n";
> }
>
> sub bar
> {
> print "bar called\n";
> }
>
> The questions I had were
> 1. To invoke a function (for e.g. foo) - what do i send across from
> the client
> command ? - daemon::foo ? A::foo ? or just foo ?
Either A::foo or foo.
Since the A package uses Exporter and includes the foo() in the
@EXPORT list whenever you "use A" the foo() gets exported to
current package ... that is an alias is made so that foo() is the
same as A::foo().
> - I guess my
> question is
> once you 'use' a package what happens to all the symbols from that
> package.
> Do they become part of the importing package ?
Depends. They do not have to.
1) If the package uses Exporter and you did not specify any
parameters to the "use A" statement all functions and variables
mentioned in @A::EXPORT are imported.
2) If you do use a parameter like this:
use A qw(foo);
then Exporter looks whether A agrees with exporting foo() = looks
whether @EXPORT_OK has an element "foo" and if it does imports
ONLY that function. Otherwise gives you an error.
3) If neither the package or the packages specified in @ISA use
Exporter or a similar module and doesn't contain import() function
.... nothing gets imported at all.
4) If the package or one of those in @ISA contains an import()
function ... then the package may export anything it likes. Read it's
docs.
> 2. A followup question is that if B and/or C had the same name
> subroutines
> as A.pm did then what would happen.
If you were running the script with -w parameter you'd get a warning:
Subroutine foo redefined at ... line ....
In that case you'd most probably want to set @EXPORT_OK and
only import the functions you want from each package.
Hope that makes sense, Jenda
=========== [EMAIL PROTECTED] == http://Jenda.Krynicky.cz ==========
There is a reason for living. There must be. I've seen it somewhere.
It's just that in the mess on my table ... and in my brain.
I can't find it.
--- me
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