Question

A coworker’s typo when calling a subref raised this strange syntax question. If I call a subref without the dereference arrow, perl dies with Not a GLOB reference. However, if the subref is called as a method on a blessed object, it runs fine.

What does this have to do with globs? And why does the method call work?

use 5.12.0;
use Try::Tiny;

my $f = sub { 'sub ref' };
my $obj = bless({}, 'Blessed');

try {
   say $f($obj); # should be $f->();
} catch { 
   say "ERROR: $_";
};

say $obj->$f();

Output:

C:\code>perl dispatch.pl
ERROR: Not a GLOB reference at dispatch.pl line 8.

sub ref

Answer 1

say, like print, accepts an optional filehandle/typeglob to direct output to, eg:

my $f = \*STDERR;
say $f ("This goes to stderr.");

I didn’t realize until now that you could do a method call on a subroutine reference, but sure enough, the perlobj man page states:

If the right side of the arrow is a scalar containing a reference to a
subroutine, then this is equivalent to calling the referenced subroutine
directly with the class name or object on the left side of the arrow as its
first argument. No lookup is done and there is no requirement that the
subroutine be defined in any package related to the class name or object on the
left side of the arrow.