SPUG: Predeclaring packages

[Christopher Howard]

On Thu, 1 Jan 2009, Yitzchak Scott-Thoennes wrote:

> On Wed, December 31, 2008 7:36 pm, Christopher Howard wrote:
>> Question: Is there a way to predeclare packages, without moving the
>> package to a separate file?
>>
>> This is my issue: When I write a script, I like to use packages to keep
>> everything nice and neat. And I like to have subs and packages after the
>> 'initializing' part of the program, so it is easy to find. So what I'm
>> doing now is something like this:
>>
>> ### EXAMPLE START ###
>
>> This doesn't work because $timer is not predeclared along with the
>> subroutines.
>
> There's something you're missing, but I'm not completely sure
> what it is.  Can you explain more what isn't working?
>
> Your example should work just fine, though the predeclarations
> are unnecessary.  Remember that first your entire script is compiled,
> including the sub definitions, and then it begins executing.
>
>

Blah!! You're right, I tried it again and it worked! (Figures...)

I did some more experimentation, and I think I know what was confusing me. 
Maybe you can confirm this: the scoping for an 'our' statement occurs 
during compiling, but actual variable assignments occur during runtime.

For example, I tried this:

### EXAMPLE START ###

use strict;
use warnings;

$Hello::greeting = 'Hello there';
Hello::sayHi();
exit(0);

package Hello;
{

our $greeting;

sub sayHi { print $greeting . "\n" }

}

### EXAMPLE END ###

This program outputs 'Hello there'. But if I move the value assignment 
inside the package, it doesn't work like I want:

### EXAMPLE START ###

use strict;
use warnings;

Hello::sayHi();
exit(0);

package Hello;
{

our $greeting = 'Hello there';

sub sayHi { print $greeting . "\n" }

}

### EXAMPLE END ###

That outputs the 'use of an unitialized variable...' warning. I'm guessing 
that is because nothing has been assigned to the package 
variable $greeting when sayHi is called, and so 'use warnings' spits out a 
warning for attempting to use an variable without first initializing it.

Am I getting it right?

-- 
Christopher Howard
http://indicium.us