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

The following code works:

File name: test.pl
#!/usr/bin/perl

use strict;
use warnings;

my $res = { 'objects'=>[ {'a'=>'1', b=>'2'} ] };
my $arr = $res->{objects};
for my $elem (@$arr) {
  print $elem->{a}."\n";
  print $elem->{b}."\n";
}

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But this code doesn't work:

File name: test2.pl
#!/usr/bin/perl

use strict;
use warnings;

my $res = { 'objects'=>[ {'a'=>'1', b=>'2'} ] };
for my $elem (@$res->{objects}) {
  print $elem->{a}."\n";
  print $elem->{b}."\n";
}

[download]

The error message I get says the following:

Not an ARRAY reference at test2.pl line 7.

How can I do this without making the copy using the intermediate $arr variable?



Thanks.




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Re: Referring to an array without copying to a separate variable first


by keszler (Priest) on Jun 26, 2013 at 21:58 UTC




    #!/usr/bin/perl

use strict;
use warnings;

my $res = { 'objects'=>[ {'a'=>'1', b=>'2'} ] };
for my $elem ( @{$res->{objects}} ) {
  print $elem->{a}."\n";
  print $elem->{b}."\n";
}

    [download]
    

Note that @{$res->{objects}} and @$res->{objects} are not the same.
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      little addendum:
      

> Note that @{$res->{objects}} and @$res->{objects} are not the same.
      

... b/c of Perl's precedence rules:
      

@$res->{objects} means @{$res}->{objects} which doesn't make sense.


      

      Cheers Rolf

       ( addicted to the Perl Programming Language) 

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"@$res->{objects} means @{$res}->{objects} which doesn't make sense."

        

        
It doesn't make sense to me either but B::Deparse seems to know what's going on:

        

        $ perl -MO=Deparse,p -e '@{$res}->{objects}'
@{$res;}->{'objects'};
-e syntax OK

        [download]
        


        
I suspect the ; after $res is the key but I'm not sure why.
I shall have to give this some more thought.

        





        

        -- Ken
        

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         which doesn't make sense.  
         Sure it does, $res just happens to be a hash
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Re: Referring to an array without copying to a separate variable first


by Anonymous Monk on Jun 27, 2013 at 00:08 UTC




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