indirect

There seems to be a general misunderstanding regarding the equivalence of
print FILEHANDLE LIST and
FILEHANDLE->print(LIST).
They are not equivalent. See ikegami's response to "Re: Optional Subroutine Arguments Like in "print FILEHANDLE LIST"". You may find that a review of print and IO::File is useful here.

Regarding what v5.36 does (and does not) allow, see the following code.

#!/usr/bin/env perl

use v5.36;
use autodie;

print "'print'\n";
print STDOUT "'print STDOUT'\n";
print STDERR "'print STDERR'\n";
STDOUT->print("STDOUT->print\n");
STDERR->print("STDERR->print\n");

my $dummy_output = 'test_indirect.out';

{
    open my $fh, '>', $dummy_output;
    print $fh "print \$fh\n";
    system cat => $dummy_output;
}

{
    open my $fh, '>', $dummy_output;
    $fh->print("\$fh->print\n");
    system cat => $dummy_output;
}

{
    my %file_handles;
    open $file_handles{test}, '>', $dummy_output;
    $file_handles{test}->print("\$file_handles{test}\n");
    system cat => $dummy_output;
}

{
    my %file_handles;
    open $file_handles{test}, '>', $dummy_output;
    print {$file_handles{test}} "print {\$file_handles{test}}\n";
    system cat => $dummy_output;
}

#{
#    my %file_handles;
#    open $file_handles{test}, '>', $dummy_output;
#    print $file_handles{test} "print \$file_handles{test}\n";
#    system cat => $dummy_output;
#}

use IO::File;

{
    my $fh = IO::File::->new($dummy_output, '>');
    print $fh "IO::File: print \$fh\n";
    system cat => $dummy_output;
}

{
    my $fh = IO::File::->new($dummy_output, '>');
    $fh->print("IO::File: \$fh->print\n");
    system cat => $dummy_output;
}

{
    #use feature 'indirect';
    my $fh = new IO::File($dummy_output, '>');
    $fh->print("indirect! IO::File: \$fh->print\n");
    system cat => $dummy_output;
}
[download]

Without Perl 5.36 you won't be able to test this, so let me demonstrate.

1. Running that as is:

   $ ./test_indirect.pl
   Bareword found where operator expected at ./test_indirect.pl line 63, 
   +near "new IO::File"
           (Do you need to predeclare new?)
   syntax error at ./test_indirect.pl line 63, near "new IO::File"
   Global symbol "$fh" requires explicit package name (did you forget to 
   +declare "my $fh"?) at ./test_indirect.pl line 64.
   Execution of ./test_indirect.pl aborted due to compilation errors.
   [download]

2. Uncommenting the use feature line:

   $ ./test_indirect.pl
   'print'
   'print STDOUT'
   'print STDERR'
   STDOUT->print
   STDERR->print
   print $fh
   $fh->print
   $file_handles{test}
   print {$file_handles{test}}
   IO::File: print $fh
   IO::File: $fh->print
   indirect! IO::File: $fh->print
   [download]

   • Discarding stderr:

     $ ./test_indirect.pl 2> /dev/null
     'print'
     'print STDOUT'
     STDOUT->print
     print $fh
     $fh->print
     $file_handles{test}
     print {$file_handles{test}}
     IO::File: print $fh
     IO::File: $fh->print
     indirect! IO::File: $fh->print
     [download]

   • Discarding stdout:

     $ ./test_indirect.pl 1> /dev/null
     'print STDERR'
     STDERR->print
     [download]

3. Uncommenting that anonymous block in the middle of the code:

   $ ./test_indirect.pl
   String found where operator expected at ./test_indirect.pl line 43, ne
   +ar "} "print \$file_handles{test}\n""
           (Missing operator before  "print \$file_handles{test}\n"?)
   syntax error at ./test_indirect.pl line 43, near "} "print \$file_hand
   +les{test}\n""
   BEGIN not safe after errors--compilation aborted at ./test_indirect.pl
   + line 47.
   [download]

multidimensional

I had to use that 25-30 years with Perl4. Except for the simplest data structures, I found the syntax to be unwieldy, hard to read, and easy to get wrong. I pretty much jumped with joy when Perl5 came out and I didn't have to use that syntax any more. Admittedly, I had 25-30 years less Perl experience back then — I might find it easier these days (but I'll never know as I have no intention of using it).