string as ref ?!?!

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

I've just found any string may be used as reference! Is anybody know where this behaviour explained in documentation? Or this is a bug? This code:

$qqq = undef();
$www = undef();
$qqq->{qwe} = 123;
printf "'%s'  '%s'  '%s'  '%s'\n",
    $qqq, $www, $qqq->{qwe}, $www->{qwe};

$eee = '';
$rrr = '';
$eee->{asd} = 456;
printf "'%s'  '%s'  '%s'  '%s'\n",
    $eee, $rrr, $eee->{asd}, $rrr->{asd};

$ttt = 'Test';
$yyy = 'Test';
$ttt->{zxc} = 789;
printf "'%s'  '%s'  '%s'  '%s'\n",
    $ttt, $yyy, $ttt->{zxc}, $yyy->{zxc};
[download]

output:

'HASH(0x81551c8)'  'HASH(0x81552d0)'  '123'  ''
''  ''  '456'  '456'
'Test'  'Test'  '789'  '789'
[download]

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Re: string as ref ?!?! by Abigail-II (Bishop) on May 10, 2004 at 10:44 UTC
It's documented exactly where you expect it be documented: in the manual page about references: `man perlref`. Abigail	[reply]
Re: Re: string as ref ?!?! by powerman (Friar) on May 10, 2004 at 11:00 UTC
Yeah, I've already realized what this is just symbolic reference... I've doublechecked `perldoc perlref`, and now, when I know what to search for I've found only one sentence about this issue: "Using a string or number as a reference produces a symbolic reference, as explained above.". And there in nothing more about this issue "above". :-( Anyway, I think a couple of examples like: `"Test"->{qwe} = 111; "Test"->[1] = 222;` [download] will be nice to have in perlref...	[reply] [d/l]
Re: string as ref ?!?! by Abigail-II (Bishop) on May 10, 2004 at 11:12 UTC
Examples from perlref dealing with symbolic references: `$name = "foo"; $$name = 1; # Sets $foo ${$name} = 2; # Sets $foo ${$name x 2} = 3; # Sets $foofoo $name->[0] = 4; # Sets $foo[0] @$name = (); # Clears @foo &$name(); # Calls &foo() (as in Perl 4) $pack = "THAT"; ${"${pack}::$name"} = 5; # Sets $THAT::foo without eval` [download] Abigail	[reply] [d/l]
Re: Re: Re: string as ref ?!?! by hardburn (Abbot) on May 10, 2004 at 19:52 UTC
I've already realized what this is just symbolic reference No, it isn't. A symbolic ref uses the string in the variable as the name of a package variable: `my $f = "foo"; our $foo = "blah"; print $$f; __OUTPUT__ blah` [download] The behavior you're seeing in your example code is autovivification. You tell Perl that you want a hashref, so you get one. This behavior is forbidden by `use strict 'refs'`. For that, you should explicitly put a hashref into the variable, such as with `my $var = { };` or `my $var = \%hash;`. ---- `: () { :\|:& };:` Note: All code is untested, unless otherwise stated	[reply] [d/l] [select]
Re: string as ref ?!?! by Hena (Friar) on May 10, 2004 at 10:46 UTC
If you use "use strict" then perl will catch those. If you notice the second groups rrr reference prints a value that has not even been set. I don't know how perl handles these situations without use strict, so i don't know why this happens.	[reply]
Re: string as ref ?!?! by Abigail-II (Bishop) on May 10, 2004 at 11:18 UTC
The second example works exactly as the third example. It doesn't matter what string we use - an empty string works the same as a string with a different value. `"" -> {foo}` [download] is the same as `${""}{foo}` [download] just like `"Bar" -> {foo}` [download] is the same as `${"Bar"}{foo}` [download] Abigail	[reply] [d/l] [select]
Re: Re: string as ref ?!?! by dave_the_m (Monsignor) on May 10, 2004 at 11:03 UTC
`$s = "aaa"; $s->{foo} = 1` [download] has the same effect as `$aaa{foo} = 1;` [download]	[reply] [d/l] [select]