Re: Getting a variable name from a reference

I think, this is not possible, because if you put a reference to a hash, the name of the hash is not saved, just it's adress.

Probably, you could save the name of the hash in the hash before referencing it.

Best regards,
perl -le "s==*F=e=>y~\*martinF~stronat~=>s~[^\w]~~g=>chop,print"

Comment on Re: Getting a variable name from a reference

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Re: Re: Getting a variable name from a reference by erikharrison (Deacon) on Mar 05, 2002 at 13:31 UTC
You're right - it can't be done without saving the name of the name of the variable and some additional jiggery pokery. At least it can't be done with a hard reference like this. The reason it can't be done is because a hard reference is just and address - so the "thingie" that the address points to might have no varable name, such as an anonymous hash: `$hashref = {'Anonymous' => 'Hash'}; #hash has no varable #name - just reference` [download] Additionally, a varable might have more than one name, if it has aliases. Back in Perl 4 (which I've never used) there were no hard refs, so you had to use variable - name - plus `eval` tricks to do reference type stuff. This might do what you want it to (warning - untested code): `#usr/bin/perl -w use strict; my %hash1 = ('A' => 1); my $hashname1 = 'hash1'; my %hash2 = ('B' => 2); my $hashname2 = 'hash2'; eval qq (print qq(Hashname: $$hashname1 Values:); print join ",",sort +keys %{$hasname1})" ); eval qq (print qq(Hashname: $$hashname1 Values:); print join ",",sort +keys %{$hasname1}) );` [download] But these kinds of eval tricks I'm not used to - and you probably shouldn't use them anyway. Also, you can't print out a memory address here, unless you add in a pair of hard refs. Cheers, Erik	[reply] [d/l] [select]

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Re: Re: Getting a variable name from a reference
by erikharrison (Deacon) on Mar 05, 2002 at 13:31 UTC

You're right - it can't be done without saving the name of the name of the variable and some additional jiggery pokery. At least it can't be done with a hard reference like this. The reason it can't be done is because a hard reference is just and address - so the "thingie" that the address points to might have no varable name, such as an anonymous hash:

$hashref = {'Anonymous' => 'Hash'}; #hash has no varable
                                    #name - just reference
[download]

Additionally, a varable might have more than one name, if it has aliases.

Back in Perl 4 (which I've never used) there were no hard refs, so you had to use variable - name - plus eval tricks to do reference type stuff. This might do what you want it to (warning - untested code):

#usr/bin/perl  -w
use strict;
my %hash1 = ('A' => 1);
my $hashname1 = 'hash1';

my %hash2 = ('B' => 2);
my $hashname2 = 'hash2';

eval qq (print qq(Hashname: $$hashname1 Values:); print join ",",sort 
+keys %{$hasname1})" );
eval qq (print qq(Hashname: $$hashname1 Values:); print join ",",sort 
+keys %{$hasname1}) );
[download]

But these kinds of eval tricks I'm not used to - and you probably shouldn't use them anyway. Also, you can't print out a memory address here, unless you add in a pair of hard refs.

[reply]
[d/l]
[select]