If you generate functions as needed with AUTOLOAD(), forward declarations make can() work correctly without you having to override it for your package.

Is there any practical application of forward declaration of subroutines?

Yes. If you have mutually recursive subroutines -- sub a calls sub b; and sub b calls sub a; -- then you need to forward declare one of them to pass strict, if you want to avoid using parens.

> mutually recursive subroutines ... if you want to avoid using parens.

As an illustration, the following doesn't work cause &b is unknown when &a is compiled.

Without strict b will be converted to string "b" and returned. (strict prohibits this behaviour of barewords.)

lanx@nc10-ubuntu:/tmp$ perl
sub a { print "a$level "; b if $level-- };
sub b { print "b$level "; a if $level-- };
$level=5;
print"\n";
a;
print"\n";
b;
__END__

a5 
b4 a3
[download]

with forward declaration

lanx@nc10-ubuntu:/tmp$ perl
sub b;
sub a { print "a$level "; b if $level-- };
sub b { print "b$level "; a if $level-- };
$level=5;
print"\n";
a;
__END__

a5 b4 a3 b2 a1 b0
[download]

Cheers Rolf

( addicted to the Perl Programming Language)

Better addressed to the OP.

---

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Hi perlaintdead,
With forward declaration of subroutine, you can omit the parentheses usage like thus:

use warnings;
use strict;

 sub printer;

 printer 'hello','world','again'; # NOTE HERE

 sub printer{
   print $_,$/ for @_;
 }
[download]

...
printer(...);
...
[download]

thanks

>perl -wE"sub foo { bar('a','b'); } sub bar($) { } foo(); say 'done'"
done

>perl -wE"sub bar($); sub foo { bar('a','b'); } sub bar($) { } foo(); 
+say 'done'"
Too many arguments for main::bar at -e line 1, near "'b')"
Execution of -e aborted due to compilation errors.
[download]