in reply to bareword and hash reference

Jep, here is something strange going on. let's send the following to the debugger:

use vars qw/%x/;

$x{test} = "very ";
$x{test}{this} = "strange";

print $x{test};
print $x{test}{this};

[download]

the second asignment causes %x not to be changed in any way. But if you make a 'V' after it, you'll see a new hash called 'very' as a symbol available with key 'this' and value 'strange'. So what's actually happening is kind of autovivified symbolic hash-refence assignment. I suppose the docs explain it somewhere but ...

Anyway: your coworker is affecting the symbol table and that is dangerous for the code. What happens if:

$x{test} = 'ENV';
$x{test}{important_key} = 'bad value';

[download]

Yes, it clobbers the environmental variable!

--
http://fruiture.de

Replies are listed 'Best First'.
Re: Re: bareword and hash reference
by mce (Curate) on Aug 22, 2002 at 14:24 UTC
    Hi,

    Yep, you are correct, and this means that 

    $a{test}="ENV";
$a{test}{this}="strange";
 
die if ENV->{this} eq $ENV{this};

    [download]
    this dies??

    I really need some coffee now.
    ---------------------------
    Dr. Mark Ceulemans
    Senior Consultant
    IT Masters, Belgium

[reply]
[d/l]

      Exactly. I conclude 'string -> {key}' equals '$string{key}' and is a symbolic reference, for 'string' is an at runtime determined name, and that's bad.

      --
      http://fruiture.de
[reply]

        fruiture++

        Using Deparse shows that that's just what happens: 

        perl -MO=Deparse scratch.pl

$a{'test'} = 'very ';
$a{'test'}{'this'} = 'strange';
print $a{'test'};
print $very {'this'};

        [download]

[reply]
[d/l]

In Section Seekers of Perl Wisdom