Hashkey stringification ... sometimes.

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

At 340460, I was replying and used the construct $self->{_$_}. I didn't quote it because hashkeys autoquote. Yet. Fletch correctly pointed out that $self->{_$_} deparses to $self->{$_->_}. Not only that, but it actually executes!

perl -e '$self->{a$_};print keys %$self, $/;'
--------
Can't call method "a" on an undefined value at -e line 1.
[download]

Going further, I get the following:

package Foo;

sub new { my $c = shift; bless \$c, $c }
sub bar { 'bar' }

package main;

$foo = Foo->new;
$x{bar$foo} = 1;
print "$_ => $x{$_}\n" for keys %x;

--------

bar => 1
[download]

Further testing shows that $x{bar $foo} and $x{$foo->bar} also work.

Now, I knew that $x{bar()} works, because that's how you get constants in there. But, method calls?

------
We are the carpenters and bricklayers of the Information Age.

Then there are Damian modules.... *sigh* ... that's not about being less-lazy -- that's about being on some really good drugs -- you know, there is no spoon. - flyingmoose

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Re: Hashkey stringification ... sometimes. by bart (Canon) on Mar 29, 2004 at 12:43 UTC
Don't rely on "automatic quoting" too much... It's only garanteed to work for barewords. `_$_` most definitely is not a bareword (= the kind of word one normally uses for variable and sub names). The same goes for the left hand side of `=>`, I'm sure `_$_` will do the same magic trick there as it did in your code... `my %hash = ( _$_ => 'foo' );` [download] this shows the following error when ran like this: Can't call method "_" on an undefined value The fact that it actually compiles, without any complaint, may be a bit unfortunate... But it's nothing out of the ordinary.	[reply] [d/l] [select]
Re: Re: Hashkey stringification ... sometimes. by dragonchild (Archbishop) on Mar 29, 2004 at 12:53 UTC
I just found an uglier case. `rob@dev01 $ perl -MO=Deparse -e '$x{_$}' Missing right curly or square bracket at -e line 1, at end of line syntax error at -e line 1, at EOF -e had compilation errors. rob@dev01 $ perl -MO=Deparse -e '$x{_$}}' $x{$}->_}; -e syntax OK` [download] Just interpose the _ and $ in $_. In almost 9 years, I've never run into that. I must have typed "{$_}" almost a million times and never mistyped it. shudders That's the kind of typo that brings grey hair to men in the teens! And, then you have `$x{y$}`, which is transliteration, `$x{s$}`, which tries to do substitution ... either it quotes or it doesn't! ------ We are the carpenters and bricklayers of the Information Age. Then there are Damian modules.... sigh* ... that's not about being less-lazy -- that's about being on some really good drugs -- you know, there is no spoon.* - flyingmoose	[reply] [d/l] [select]
Re: Hashkey stringification ... sometimes. by broquaint (Abbot) on Mar 29, 2004 at 12:42 UTC
See. indirect method calling syntax and tye's Indirect object syntax (RE: Beginnings of Online CGI Course) on why it is icky (as your case aptly demonstrates). HTH `_________ broquaint`	[reply]
Re: Hashkey stringification ... sometimes. by QM (Parson) on Mar 29, 2004 at 14:15 UTC
For those just tuning in to Perl, notice that `_` (underline, underbar, or just bar) is a legal identifier, hence a legal sub name and method name. -QM -- Quantum Mechanics: The dreams stuff is made of	[reply] [d/l]
Re: Re: Hashkey stringification ... sometimes. by Anomynous Monk (Scribe) on Mar 30, 2004 at 02:13 UTC
But remember that it defaults to package main if no explicit package is specified, whether you use $_, @_, %_, or _: `$ perl -we'package Foo; sub _ { print "hi" } package Bar; _; main::_' hihi` [download]	[reply] [d/l]