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

in reply to Referring to an array without copying to a separate variable first

#!/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.

Comment on Re: Referring to an array without copying to a separate variable first Select or Download Code

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Re^2: Referring to an array without copying to a separate variable first by LanX (Saint) on Jun 26, 2013 at 22:06 UTC
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)	[reply] [d/l] [select]
Re^3: Referring to an array without copying to a separate variable first by kcott (Archbishop) on Jun 27, 2013 at 09:33 UTC
"`@$res->{objects}` means `@{$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	[reply] [d/l] [select]
Re^4: Referring to an array without copying to a separate variable first by LanX (Saint) on Jun 27, 2013 at 10:04 UTC
> ... but B::Deparse seems to know what's going on: ... B::Deparse can't help here, cause it's a runtime error and not a syntax problem. > ... I suspect the ; after $res is the key ... The ';' you are seeing is an indicator that `%{ }` and alike are effectively `do { }` blocks plus dereferencing. `lanx@nc10-ubuntu:~$ perl -e '$r={a=>1};print %{$r;},"\n"' a1 lanx@nc10-ubuntu:~$ perl -MO=Deparse,p -e '$r={a=>1};print %{$r;},"\n" +' $r = {'a', 1}; print %{$r;}, "\n"; -e syntax OK lanx@nc10-ubuntu:~$ perl -MO=Deparse,p -e 'print %{ $r={a=>1};$r; },"\ +n"' print %{$r = {'a', 1}; $r;}, "\n"; -e syntax OK lanx@nc10-ubuntu:~$ perl -e 'print %{ $r={a=>1};$r; },"\n"' a1` [download] Interesting, well spotted! =) UDPATE Reminds me of this old trick to have code executed within interpolation `DB<100> print " @{ [ 1..10 ] } " 1 2 3 4 5 6 7 8 9 10` [download] maybe clearer `DB<106> print " @{ $a++; [1..$a ] } " 1 DB<107> print " @{ $a++; [1..$a ] } " 1 2 DB<108> print " @{ $a++; [1..$a ] } " 1 2 3` [download] Cheers Rolf ( addicted to the Perl Programming Language)	[reply] [d/l] [select]
Re^5: Referring to an array without copying to a separate variable first by kcott (Archbishop) on Jun 30, 2013 at 05:07 UTC
Re^3: Referring to an array without copying to a separate variable first by Anonymous Monk on Jun 27, 2013 at 00:06 UTC
which doesn't make sense. Sure it does, $res just happens to be a hash	[reply]
Re^4: Referring to an array without copying to a separate variable first by LanX (Saint) on Jun 27, 2013 at 00:14 UTC
> Sure it does, $res just happens to be a hash No it never does, since the code `@{$res}->{objects}` tries to dereference a hash-ref not an array. But interestingly this magically (?) works: `DB<112> @a="a".."d" => ("a", "b", "c", "d") DB<113> @a->[2] => "c"` [download] aaaah! =) `DB<114> use warnings; @a->[2] Using an array as a reference is deprecated ...` [download] Cheers Rolf ( addicted to the Perl Programming Language)	[reply] [d/l] [select]

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