using the perl debugger...

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

the two following bits of code produce to different outputs when the main variable '%args' is viewed with the 'x' command in the debugger.

i'm hoping that someone can explain what i'm seeing.

run a script with the following code

    
    my %args;
    $args{'expr'} = \['booya' 'kada'];
[download]

then perform 'x \%args'...you'll see this:

  DB<2> x \%args
0  HASH(0x1cb3778)
   'expr' => REF(0x1a35d54)
      -> ARRAY(0x1ca0124)          (WHY AN ARROW?)
            0  'booya'
            1  'kada'
[download]

then run the followin in a script:

    my %args;
    my @ary;
    @ary = ['booya', 'kada'];
    $args{'expr'} = \@ary;
[download]

in this case 'x \%args' produces:

  DB<3> x \%args
0  HASH(0x1cb3778)
   'expr' => ARRAY(0x1cb3844)
      0  ARRAY(0x1cea068)          (WHY A ZERO?)
         0  'booya'
         1  'kada'
[download]

so my question is this: what to the ARROW & ZERO signify and what is the difference. i'm guessing its related to anonymity, but i don't know and i believe there is a gem of knowledge here i don't want to lose.

i suppose a second question is this: where could i have found this answer myself - any documentation that explains debugger command outputs (in detail).

thanks in advance, nebbish

Comment on using the perl debugger... Select or Download Code

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Re: using the perl debugger... by salva (Canon) on Apr 03, 2006 at 19:44 UTC
you are really creating different structures, Data::Dumper shows the difference clearly: `$VAR1 = { 'expr' => \[ 'booya', 'kada' ] }; $VAR1 = { 'expr' => [ [ 'booya', 'kada' ] ] };` [download] I thing you are confused about the way array references are created in perl. Probably, you would like to use... `my %args; $args{'expr'} = ['booya' 'kada']; # no \ required here` [download] or `my %args; my @ary; @ary = ('booya', 'kada'); # use () instead of [] $args{'expr'} = \@ary;` [download] to create `$VAR1 = { 'expr' => [ 'booya', 'kada' ] };` [download]	[reply] [d/l] [select]
Re: using the perl debugger... by gaal (Parson) on Apr 03, 2006 at 19:50 UTC
Look at the prints for booya and kada: they have 0 and 1 preceding them. Why? Because those are the indices in an array. In the first dump you gave, the container that held a reference to `['booya', 'kada']` had no interesting type of its own, therefore its stringification was REF (ref-to-a-ref). In the second case, you had an array container, and the first element of the array was a reference to `['booya', 'kada']`. The second case, with the 0, should be clear: the 0th element of the array pointed to by `\@ary` is the anonymous array. In the second case, there is no index, there's just a straight reference. That is signified by an arrow. I think this is the kind of thing you either don't worry about, or deduce, or read the source for. :-)	[reply] [d/l] [select]
Re: using the perl debugger... by nebbish (Novice) on Apr 04, 2006 at 17:32 UTC
thanks for your input guys. based on that i read more on the () and [] operators, learned how to use data::dumper (pardon the pun), and got that much stronger with references in perl. thanks again, nebbish	[reply]