printing code references
 

how do i print the name of the subroutine to which a code ref points?

#!/opt/vdops/bin/perl
use strict;
use warnings;

my $ref;
$ref = \&foo;
print "&$ref\n";

sub foo {
# Do nothing
}

guru% ./test
&CODE(0x815bed0)
guru%


I would like to see "&foo" instead of "&CODE(0x815bed0)".

--sk

stuart kendrick
fhcrc

Re: printing code references
 

Stuart Kendrick <skendric@fhcrc.org> wrote in comp.lang.perl.misc:
> how do i print the name of the subroutine to which a code ref points?
>
> #!/opt/vdops/bin/perl
> use strict;
> use warnings;
>
> my $ref;
> $ref = \&foo;
> print "&$ref\n";
>
> sub foo {
> # Do nothing
> }
>
> guru% ./test
> &CODE(0x815bed0)
> guru%
>
>
> I would like to see "&foo" instead of "&CODE(0x815bed0)".

You can't. A sub can be anonymous, it can also be reachable through
more than one name. In the first case, there simply is no name, in
the second, which one should it print?

When a sub is called, the name though which it has been called is
available through the caller() function, but that's doesn't help
with a static coderef. Short of a comprehensive search through
all packages, there is no way to determine if a coderef has names.
(It can be done, and since it can be done, there must be a module...)

Anno

Re: printing code references
 

Anno Siegel <anno4000@lublin.zrz.tu-berlin.de> wrote:
>Stuart Kendrick <skendric@fhcrc.org> wrote in comp.lang.perl.misc:
>>
>> I would like to see "&foo" instead of "&CODE(0x815bed0)".
>
>You can't. A sub can be anonymous, it can also be reachable through
>more than one name. In the first case, there simply is no name, in
>the second, which one should it print?

You can, actually - the debugger manages it. It just makes up a name
for anon subs:

DB<1> sub a { print "Hello" }

DB<2> $a = \&a

DB<3> x $a
0 CODE(0x31f178)
-> &main::a in (eval 6)[/home/mjtg/perl-5.8.1-RC4/lib/perl5db.pl:618]:2-2
DB<4> $a = sub { print "Goodbye" }

DB<5> x $a
0 CODE(0x336c30)
-> &main::__ANON__[(eval 10)[/home/mjtg/perl-5.8.1-RC4/lib/perl5db.pl:618]:2] in (eval 10)[/home/mjtg/perl-5.8.1-RC4/lib/perl5db.pl:618]:2-2
DB<6>

To see how the trick is performed, rummage in the source of the debugger.


Mike Guy