Defining a hash key for later use

amw1 has asked for the wisdom of the Perl Monks concerning the following question:

I'm building a data structure from a config file that looks roughly like this (doing a single pass populating hash entries as they are encountered, not looking ahead):

# Define a page
page <page key>
{
   toolbar standard;
};
# Define a standard toolbar
toolbar standard
{
   item
   {
      <item config>
   };
};
[download]

When I encounter toolbar standard; in the page config I want to create a blank hash key that will get filled later with the actual definition of toolbar standard. I've tried the following:

# Encounter the toolbar standard; line in the page config

# Doesn't actually do anything
$page->{<page_key>}{'toolbar'} = $toolbar->{'standard'};

# complains about standard getting re-defined
$toolbar->{'standard'} ||= {};  # also tried undef and dummy value ins
+tead of {} with no luck
$page->{<page_key>}{'toolbar'} = $toolbar->{'standard'};

# $toolbar->{'standard'} is actually populated sometime after I proces
+s $page->{<page_key>}
[download]

Is there any way to get the toolbar def in the page config point to a bucket that will be filled when the toolbar section is processed?

Comment on Defining a hash key for later use Select or Download Code

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Re: Defining a hash key for later use by eieio (Pilgrim) on Feb 01, 2005 at 16:52 UTC
The following seems to work for me. I'm storing a reference in the page hash rather than a value. When `$toolbar->{'standard'}` is later populated, the value will change and the reference that is stored in the page hash will point to the new value. `$page->{'page_key'}{'toolbar'} = \$toolbarRef->{'standard'}; $toolbar->{'standard'} = 7; print ${$page->{'page_key'}{'toolbar'}}; #prints 7` [download]	[reply] [d/l] [select]
Re^2: Defining a hash key for later use by amw1 (Friar) on Feb 01, 2005 at 16:56 UTC
That appears to work. I had a hole elsewhere. sigh I should have done a small test case rather than working in my main program. Thanks.	[reply]
Re: Defining a hash key for later use by Animator (Hermit) on Feb 01, 2005 at 16:45 UTC
So what you want to do is just create an element? and set it's value to undef? Then you could simply do `$page->{....}{'toolbar'};` then the key will be created...	[reply] [d/l]
Re^2: Defining a hash key for later use by amw1 (Friar) on Feb 01, 2005 at 16:51 UTC
I've also just tried to set: `$page->{...}{'toolbar'}{'standard'} = $toolbar->{'standard'};` [download] before $toolbar->{'standard'} gets defined but it doesn't appear to work. I was expecting it to work as well. I may have misstated a detail on the problem. The structure lays out a little more like this: `# $struct->{'toolbar'}{'standard'} does not exist at # this point. $struct->{'toolbar'} may or may not exist $struct->{'page'}{...}{'toolbar'}{'standard'} = $struct->{'toolbar'}{' +standard'};` [download] This is more complete.	[reply] [d/l] [select]