I didn't say it was invalid, I said it was perl4 style with gotchas. I don't think I've ever seen a Seeker of Perl Wisdom who uses it and is aware of its side-effects. :P It whispers cargo-cult and cgi-lib.pl to me.

I'm not for sure a model for others perl programmers, but i still use it, and i'm aware of what i'm doing (disable prototypes and pass current @_ to the sub, but just in case of ⊂ ), to visually tell at glance locally (same file) defined subroutines from others imported by used modules.

perlsub states:

The & is optional in modern Perl, as are parentheses if the subroutine has been predeclared. The & is not optional..

L*

There are no rules, there are no thumbs..
Reinvent the wheel, then learn The Wheel; may be one day you reinvent one of THE WHEELS.

> to visually tell at glance locally (same file) defined subroutines

That seems to be your convention, but Perl allows you to &-sigilize an imported subroutine:

#!/usr/bin/perl
use warnings;
use strict;
use feature qw{ say };

use POSIX;

say &ceil(1.23);
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($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,
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