Re: Reference madness

The problem is you are using global variables, in particular global @say. The assignment

                @say = keys %{$h{$kind}{$name}};
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changes the contents of the array, but \@say remains the same, i.e. what you assign to $b{$name} is still the same array.

The common solution to the problem is to declare a new array for each iteration of the loop, i.e. use

    my @say = keys %{$h{$kind}{$name}};
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which will create a fresh new array with different \@say for each iteration of the loop;

or create an anonymous array:

$b{$name} = [ @say ];
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($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,
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Re^2: Reference madness
by sdani (Novice) on Jul 31, 2017 at 12:58 UTC

"bark", "woof"

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Re^3: Reference madness

by choroba (Cardinal) on Jul 31, 2017 at 13:32 UTC

> I would say it's a quite unexpected behaviour (at least by me)

Once you understand how references work, there's no surprise. \@say is the reference to @say, when you change the contents of @say, \@say still points to @say, i.e. to the new contents of it. When you store a reference, you don't store the contents.

> when I dump \@say, it prints out the expected results (different for each animal)

Of course. Otherwise, changing @say would have to edit the already printed output.

($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,
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Re^3: Reference madness

by Athanasius (Archbishop) on Jul 31, 2017 at 13:39 UTC

Hello sdani,

I would say it's a quite unexpected behaviour..., because when I dump \@say, it prints out the expected results...

That’s because Data::Dumper (like Data::Dump) applies a dereferencing operation to its argument if that argument is a reference. This is usually what you want; but to avoid it, just print the variable instead:

23:27 >perl -MData::Dumper -wE "my @a = qw( a e i o u ); print Dumper(
+\@a); print \@a;"
$VAR1 = [
          'a',
          'e',
          'i',
          'o',
          'u'
        ];
ARRAY(0x4d2ec8)
23:27 >
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Note the square brackets in the output from Data::Dumper: they denote an anonymous array reference. See perlreftut.

Hope that helps,

Athanasius <°(((>< contra mundum Iustus alius egestas vitae, eros Piratica,

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Re^3: Reference madness (room/address analogy)

by LanX (Saint) on Jul 31, 2017 at 14:55 UTC

You are changing the inhabitants of always the same (hotel) room and every time storing the address to this one room.

Your dumps inside the loop only show the temporary inhabitants, but your last dump will only show the last inhabitants for always the same address.

Using my will tell Perl to always create a new proper room with a unique address.

Clearer?

Cheers Rolf
_{(addicted to the Perl Programming Language and ☆☆☆☆ :)

Je suis Charlie!}