A new episode in the series: "Yes, Perl can do!"

I recently had a discussion with a fellow perlmonger about a 3h video¹ about meta-programming in Python thanks to so called decorators. (something like advice in LISP)

So my reply was

Great, but what exactly are the benefits over attributes and type-glob manipulation in Perl?

His long reply can be summarized with something like

• Attributes are very difficult to handle
• "Nobody" understands them
• no good tutorials
• In Python decorators are first class objects with very short elegant code
• glob manipulations in Perl are cryptic
• Attributes are rarely used in Perl
• While typical use cases in Python are
  • memoization,
  • debugging,
  • logging
  • CLI wrapping,
  • route-wrapper for web-applications
  • ...

So I accepted the challenge to prove him wrong:

Taking this (rather stupid) example from SO:

def makebold(fn):
    def wrapped():
        return "<b>" + fn() + "</b>"
    return wrapped

def makeitalic(fn):
    def wrapped():
        return "<i>" + fn() + "</i>"
    return wrapped

@makebold
@makeitalic
def hello():
    return "hello world"

print hello() ## returns <b><i>hello world</i></b>
[download]

I hacked this code

use strict;
use warnings;

use Data::Dumper qw'Dumper';
use Attribute::Handlers;  
use feature 'say';

sub wrap {
  my ($glob,$c_wrapper) = @_;
  no warnings 'redefine';
  *$glob = $c_wrapper;
}

sub BOLD :ATTR {
  my ($pkg,$glob,$ref) = @_;
  
  wrap $glob => sub { "<b>" . $ref->() . "</b>" };
}

sub ITALIC :ATTR {
  my ($pkg,$glob,$ref) = @_;

  wrap $glob => sub { "<i>" . $ref->() . "</i>"};
}

sub hello :ITALIC :BOLD  {
    return "hello world";
}

say hello();
__END__
<b><i>hello World</i></b>
[download]

IMHO the Perl code is already better readable and can even be further improved with more syntactic sugar.

Not every decorator really needs to wrap code, abstracting it into a function wrap from an imported module seems reasonable (Python-folks always return the identical function-ref to handle this)

My friend was impressed, but maybe he wasn't critical enough.

Here my questions :

• Did I miss something?
• Does Attribute::Handlers have traps to be avoided?
• Why do we ignore attributes?
• Why don't we adapt (i.e. steal) good use cases from Python or LISP

Actually I wanted to meditate more about the issue and refine the code before posting, but I'm quite busy at the moment and the risk to forget this task in a drawer is quite high.

So following the release often paradigm I just posted my raw results...

At least I hope you have now good arguments, if someone claims Python was superior because of decorators!

¹) OMG 8-|

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