Re-using a hash value in same hash?

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

Not sure if I am out of my mind by trying or if I just cant grasp what I am trying to do, but here goes.

What I am trying to do involves a hash of hashes and subroutines. I am running the program with -w and use strict (learned that one a long time ago :) It's better explained after a snippet:

my %HoH = (
 yadda1 => {
    key1 => "value1",
    key2 => &GetValue, # returns date string
    key3 => &Compare($var1,$HoH{yadda1}{key2}),
 },
 yadda2 => {
    key1 => "value1",
    key2 => &GetValue, # returns date string
    key3 => &Compare($var1,$HoH{yadda2}{key2}),
 },
);
[download]

The problem exists when I try to get the value from key2 into the subroutine being called *IN* key3. It tells me "Global symbol "%HoH" requires explicit package name ... ". The hash has been declared, but I am basically calling it from within itself - is this not possible? If it is, what am I doing wrong?

- oakley
Embracing insanity - one twitch at a time >:)

Comment on Re-using a hash value in same hash? Download Code

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Re: Re-using a hash value in same hash? by merlyn (Sage) on Mar 06, 2001 at 00:15 UTC
The hash `%HoH` is not declared until the end of the statement in which it appears. That lets you do things like: `my $this = $this * 2; # use outer $this to initialize local inner $thi +s` [download] But it's getting in your way here. You'll need to set up the hash as a series of actions, not as an initialization. -- Randal L. Schwartz, Perl hacker	[reply] [d/l]
Re: Re-using a hash value in same hash? by chipmunk (Parson) on Mar 06, 2001 at 00:24 UTC
When you declare a variable with `my`, the declaration takes effect for the following statement. This allows you to do things like: `#!perl my $x = 'outer'; { my $x = $x; # new $x, copy value from old $x print "$x\n"; $x = 'inner'; print "$x\n"; } print "$x\n"; __END__` [download] In your code, you need to declare %HoH before you reference it. For example: `my %HoH; %HoH = ( yadda1 => { key1 => "value1", key2 => &GetValue, # returns date string key3 => &Compare($var1,$HoH{yadda1}{key2}), }, yadda2 => { key1 => "value1", key2 => &GetValue, # returns date string key3 => &Compare($var1,$HoH{yadda2}{key2}), }, );` [download] That will avoid the warning from strict, but it doesn't actually solve the problem. When you assign to a variable, if you refer to that same variable on the RHS of the assignment, you will get the old value of the variable. This is a lot like what happens with my: `my %HoH = ( key1 => 'first' ); %HoH = ( key1 => 'second', key2 => $HoH{key1}, );` [download] $HoH{key2} will be 'first', because that was the value of $HoH{key1} when the RHS of the assignment was evaluated. I would suggest you do something like this: `my $date_string = &GetValue; my $comparison = &Compare($var1, $date_string); %HoH = ( yadda1 => { key1 => "value1", key2 => $date_string, key3 => $comparison, }, yadda2 => { key1 => "value1", key2 => $date_string key3 => $comparison, }, );` [download]	[reply] [d/l] [select]
(tye)Re: Re-using a hash value in same hash? by tye (Sage) on Mar 06, 2001 at 00:20 UTC
`my %HoH = ( yadda1 => { key1 => "value1", key2 => &GetValue, # returns date string }, yadda2 => { key1 => "value1", key2 => &GetValue, # returns date string }, ); for( keys %HoH ) { $HoH{$_}{key3}= &Compare( $var1, $HoH{$_}{key2} ); }` [download] is one way to do it. - tye (but my friends call me "Tye")	[reply] [d/l]
Re: Re-using a hash value in same hash? by boo_radley (Parson) on Mar 06, 2001 at 00:22 UTC
Since I was starchy in the CB, I'll put in my 2 cents. I think the problem is occurring because you're trying to reference HoH during it's creation. -deletia- update well, shoot. :) you got the same piece of advice ~~three~~ four times. So there you go.	[reply]