in reply to Put references to array of hash elements in an array

> What am I doing wrong, please?

Precedence!

$$age_ref[1] means ${$age_ref}[1] not ${$age_ref[1]} 

@AoH =
(
        { name => Adam, age => 0 },
        { name => Bob,  age => 10 },
        { name => Cat,  age => 20 }
);

@age_ref = (\$AoH[0]{age},\$AoH[2]{age});
print "\${\$age_ref[1]} = ${$age_ref[1]} =  $AoH[2]{age}\n";
# prints ${$age_ref[1]} = 20 =  20

[download]

HTH! :)

Cheers Rolf
(addicted to the Perl Programming Language :)
Wikisyntax for the Monastery FootballPerl is like chess, only without the dice

Replies are listed 'Best First'.
Re^2: Put references to array of hash elements in an array
by tel2 (Pilgrim) on Aug 03, 2018 at 04:52 UTC
    Actually I'm still having problems in my real code.

    When reading a table with DBI into @age_ref, should this syntax update the age values in @AoH? 

    @age_ref = (\$AoH[0]{age},\$AoH[2]{age});
while (@age_ref = \$sth->fetchrow_array)

    [download]

    The problem is, the age values in the @HoA are not being updated as a result of the above code.
    Any ideas on how to make that work, please?

[reply]
[d/l]
      References work the other way round. \$AoH[0]{age} is a reference to the value stored under age, i.e. something like \42, it's no longer connected to the structure it came from.

      You need to store the references in the @AoH if you want it to reflect the changes: 

      #!/usr/bin/perl
use warnings;
use strict;

my @AoH;
my @age_ref = (42, 33);

@AoH = (
    { age => \$age_ref[0] },
    {},
    { age => \$age_ref[1] },
);


use Data::Dumper; print Dumper \@age_ref;

@age_ref = (1, 2);

use Data::Dumper; print Dumper \@AoH;

      [download]

      ($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,

      [download]
[reply]
[d/l]
[select]
        Thanks for that, choroba,

        If references work the other way round (i.e. I need to store the reference in the @AoH), then why does this code update the @AoH?:

        @AoH =
(
        { name => Adam, age => 0 },
        { name => Bob,  age => 10 },
        { name => Cat,  age => 20 }
);

@age_ref = (\$AoH[0]{age},\$AoH[2]{age});
${$age_ref[1]} = 23;
print "\$AoH[2]{age} = $AoH[2]{age}\n";
# The above prints '$AoH[2]{age} = 23'

        [download]

        Thanks.
        Tel2

[reply]
[d/l]
      I think you want to look into DBI's ->bind_col and ->bind_columns instead of these hacks.

      Cheers Rolf
      (addicted to the Perl Programming Language :)
      Wikisyntax for the Monastery FootballPerl is like chess, only without the dice

[reply]
        I didn't know they were hacks, Rolf, but thanks for the tips.
[reply]
Re^2: Put references to array of hash elements in an array
by tel2 (Pilgrim) on Aug 03, 2018 at 03:22 UTC
    Orsum!

    Thanks heaps for the speedy and useful reply, Rolf!  Feel free to take a pay rise.

[reply]
      > Feel free to take a pay rise.

      Send me the scalps of three Pythonistas and we are even! ;-)

      Cheers Rolf
      (addicted to the Perl Programming Language :)
      Wikisyntax for the Monastery FootballPerl is like chess, only without the dice

[reply]
        Sounds like a reasonable deal.  Hope we don't get caught by any Hate Speech laws.  Or we might just get called racist or languageist.
[reply]

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