Creating a hash with key generated by a sub?

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

Hello All...

I'm having a problem generating hash keys using a sub. I'm pretty sure that this is a syntactic error and while I could easily "do it another way" I'm just curious as to why this occurs....

Let's set it all up:

use Digest::MD5 qw(md5_hex);
use strict; 
use warnings;

my $secret = "applepie";
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Here's the sub function:

sub get_md5 
{
 md5_hex("$secret" . "$_")
};
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This works great...

my @array          = qw(foo bar baz);
my %md5_other_hash = (map {&get_md5, $_ } @array);
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Not this though:

my %md5_hash       = ( &get_md5('foo')  => "foo",
                       &get_md5('bar')  => "bar",
                       &get_md5('bar')  => "baz",
);
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But Why?

Whereas, here we have no problem...

print &get_md5('foo');
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Anyone care to help me understand what's going on here? I intuitively think it should be fine.... which is why I ask...

Many thanks in advance,

Cheers

Comment on Creating a hash with key generated by a sub? Select or Download Code

Replies are listed 'Best First'.
Re: Creating a hash with key generated by a sub? by gaal (Parson) on Nov 12, 2004 at 13:57 UTC
Note that your code here: `sub get_md5 { md5_hex("$secret" . "$_") };` [download] uses two globals and would probably be better written to use parameters: `sub get_md5 { my($my_secret, $data) = @_; md5_hex($my_secret . $data); };` [download]	[reply] [d/l] [select]
Re: Creating a hash with key generated by a sub? by steves (Curate) on Nov 12, 2004 at 13:11 UTC
You had a few simple errors. This works: `use Digest::MD5 qw(md5_hex); use strict; use warnings; my $secret = "applepie"; sub get_md5 { md5_hex("$secret" . "$_[0]") }; my @array = qw(foo bar baz); my %md5_hash_broken = (map {&get_md5($_) => $_} @array); my %md5_hash = ( &get_md5('foo') => "foo", &get_md5('bar') => "bar", &get_md5('fubar') => "baz", ); my ($x, $y); while (($x, $y) = each %md5_hash) { print "$x => $y\n"; }` [download] The errors (see my changes): I got a warning on the use of $_ in get_md5(); Your map was not passing an argument to get_md5(); Your hash called get_md5() with the argument bar twice.	[reply] [d/l]
Re^2: Creating a hash with key generated by a sub? by smullis (Pilgrim) on Nov 12, 2004 at 13:21 UTC
Thanks for this steves... One point of interest - I thought that `$_` was implicitly passed to `map`? The `%blah = (map {&get_md5, $_} @array);` worked for me fine... Cheers, SM	[reply] [d/l] [select]
Re^3: Creating a hash with key generated by a sub? by steves (Curate) on Nov 12, 2004 at 13:27 UTC
I should clarify: In other places, get_md5() is passed with one argument, which I assumed you wanted concatenated to $secret to make the key. The way map was originally set up, it was not passing anything to get_md5() -- it was calling it with no arguments and using $_ as the hash value. Unless I'm missing something ...	[reply]
Re: Creating a hash with key generated by a sub? by dragonchild (Archbishop) on Nov 12, 2004 at 12:58 UTC
What doesn't work? It looks just fine to me ... Being right, does not endow the right to be rude; politeness costs nothing. Being unknowing, is not the same as being stupid. Expressing a contrary opinion, whether to the individual or the group, is more often a sign of deeper thought than of cantankerous belligerence. Do not mistake your goals as the only goals; your opinion as the only opinion; your confidence as correctness. Saying you know better is not the same as explaining you know better.	[reply]
Re^2: Creating a hash with key generated by a sub? by smullis (Pilgrim) on Nov 12, 2004 at 13:07 UTC
AAAAAARRRRRGGGGGHHHH!!!!!!!!!! Dragonchild, you are - of course - completely correct I am, quite simply, being an ase. FYI - my original code, before I copied it into PM - all neat and tidy - didn't quote the hash value. THAT's where the error was from.... I suppose I can take solace in the fact my intuition was correct - I've just got to learn to trust it a bit more!! Cheers SM ...smullis puts his tail between his legs and runs off to hide....*	[reply]

AAAAAARRRRRGGGGGHHHH!!!!!!!!!!