Re^2: Best Hash Practices?

> that autovivication doesn't happen when you simply check wether a hash key exists or is true.

unfortunately not that simple!

use strict;   # or die
use warnings; # or die
 
my %hash = (
   cogito   => "ergo sum"   # I think, so I exist
);
 
if (exists $hash{absum}{absum}) {
    print "Absum exists.";
} else {
    print "Absum doesn't exist.\n";
    # which would explain it's name...
}
 
print "Keys in the hash: ", join(" :: ", keys %hash), "\n";
[download]

output

/usr/bin/perl -w /home/lanx/tst.pl 
Absum doesn't exist.
Keys in the hash: cogito :: absum
[download]

Cheers Rolf

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Re^3: Best Hash Practices? by muba (Priest) on Oct 10, 2009 at 02:16 UTC
unfortunately not that simple! `if (exists $hash{absum}{absum})` [download] Ah, yes. But note how that syntax implies a `->` operator, as ikegami described elsewhere in this thread, and it is that operator which makes `$hash{absum}` come into existance. Of course it is funny to see how `exists` still thinks `$hash{absum}` doesn't exist, however, not so funny anymore when you realize that `exists` really tries to check the existance of `$hash{absum}->{absum}` here. So `exists` is right and the information in that `print` statement is factually wrong. It should state `print "Absum->absum doesn't exist\n"` or something similar meaning the same.	[reply] [d/l] [select]

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Re^3: Best Hash Practices?
by muba (Priest) on Oct 10, 2009 at 02:16 UTC

unfortunately not that simple!


if (exists $hash{absum}{absum})
[download]

Ah, yes. But note how that syntax implies a -> operator, as ikegami described elsewhere in this thread, and it is that operator which makes $hash{absum} come into existance. Of course it is funny to see how exists still thinks $hash{absum} doesn't exist, however, not so funny anymore when you realize that exists really tries to check the existance of $hash{absum}->{absum} here. So exists is right and the information in that print statement is factually wrong. It should state print "Absum->absum doesn't exist\n" or something similar meaning the same.

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