Now I expected one change to the code and one optional improvement that I could now make. However along with these I got two extra enforced changes.

Re-opening a class

First the expected change to re-opening a class:

class Ninja is also { ... }

# is now...

augment class Ninja { ... }

However for this to work I needed to add the following:

use MONKEY_TYPING;

A pragmatic addition. If you’re gonna shoot yourself in the foot then at least you have to prepare for it in advance

NB. Rakudo nicely gave me a fatal warning when I tried to re-open the class and politely told me that use MONKEY_TYPING was needed it I wanted to augment class Ninja.

Applying a role to an object (instance)

Now the next change was optional but it was a more succinct way to add a role to an object. Previously I had to create a role and then apply it to object:

role ThrowStar {
  method throw_star { say "throwing star" }
}

$drew does ThrowStar;

Now with Rakudo Star I can apply an anonymous role directly:

$drew does role {
  method throw_star { say "throwing star" }
};

Something I didn’t expect

The final change to the code was something unexpected. I got the following error:

===SORRY!===
Quoted method name requires parenthesized arguments at line 50, near "; # =>"


This was tied to this line of code:

$drew.'battle_cry';     # => Drew says zing!!!

I am not sure if this is a change to Perl6 spec but it now requires extra parenthesis:

$drew.'battle_cry'();     # => Drew says zing!!!

… and finally

My original post from beginning of the year was me just kicking the Rakudo tyres. I’m now looking forward to taking it out for a proper test drive around the block

Below is the complete revised code:

use v6;
use MONKEY_TYPING;

class Ninja {
    has Str $.name is rw;
}

my Ninja $drew .= new( name => 'Drew' );
my Ninja $adam .= new( name => 'Adam' );


###########################################################
# Reopen Ninja class ("is also" does the biz) 
# and add 'battle_cry' method

augment class Ninja {
    method battle_cry {
        say $.name ~ ' says zing!!!'; 
    }
}

$drew.battle_cry;   # => Drew says zing!!!
$adam.battle_cry;   # => Adam says zing!!!


###########################################################
# add 'throw_star' method to $drew object by 
# applying ("does") role to it (Singleton method)

$drew does role {
    method throw_star { say "throwing star" }
};

$drew.throw_star;     # => throwing a star


###########################################################
# call method dynamically

$drew.'battle_cry'();     # => Drew says zing!!!


###########################################################
# add "colour" method closing over $colour_name (ie. closure):

my $colour_name = 'black';

augment class Ninja {
    method colour { say "{$.name}'s colour is $colour_name" }
}

$drew.colour;    # => Drew's colour is black
$adam.colour;    # => Adam's colour is black
 
 
###########################################################

# "defining a method dynamically on an instance that closes 
# over local scope and accesses the instance’s state"
#
# Opps - Class method slipped in while working it out.
# $drew.^add_method() does a singleton method.. nice!

my $sword_symbol = '********';

$drew.^add_method( 'swing', method ( Str $sound_effect ) { 
    say "$.name: $sword_symbol $sound_effect";
} );

$drew.swing( 'slash!!' );

Happy halloween!

/I3az/

How would it look in Perl 6?

Well here goes, the complete example written in Perl 6 which runs on Rakudo, an implementation of the Perl 6 spec on the Parrot VM:

use v6;

class Ninja {
    has Str $.name is rw;
}

my Ninja $drew .= new( name => 'Drew' );
my Ninja $adam .= new( name => 'Adam' );


###########################################################
# Reopen Ninja class ("is also" does the biz) 
# and add 'battle_cry' method

class Ninja is also {    
    method battle_cry {
        say $.name ~ ' says zing!!!'; 
    }
}

$drew.battle_cry;   # => Drew says zing!!!
$adam.battle_cry;   # => Adam says zing!!!


###########################################################
# add 'throw_star' method to $drew object by creating
# and applying ("does") role to it (Singleton method)

role ThrowStar {
    method throw_star { say "throwing star" }
}

$drew does ThrowStar;
$drew.throw_star;     # => throwing a star


###########################################################
# call method dynamically: $obj.'method_name' or $obj.$method

$drew.'battle_cry';     # => Drew says zing!!!


###########################################################
# add "colour" method closing over $colour_name (ie. closure):

my $colour_name = 'black';

class Ninja is also {
    method colour { say "{$.name}'s colour is {$colour_name} " }
}

$drew.colour;    # => Drew's colour is black
$adam.colour;    # => Adam's colour is black


###########################################################

# "defining a method dynamically on an instance that closes 
# over local scope and accesses the instance’s state"

my $sword_symbol = '********';

$drew.^add_method( 'swing', method ( Str $sound_effect ) { 
    say "{$.name}: {$sword_symbol} {$sound_effect}";
});

$drew.swing( 'slash!!' );    # => Drew: ********* slash!!

Of all the examples (in Perl 5 / Moose, Ruby, Javascript & Python) I think this one is the most clean and intuitive. Perl 6 has a good future if it keeps this up!

And it all went surprising smoothly. There were a couple of bumps in my Perl 6 road but these are all connected to the flux between the Perl 6 spec, Rakudo and knowing what info you find on the web is still accurate (or not).

First bump was how to re-open a class. Most Perl 6 documentation implied that classes were always open (unless is final was used). This no longer seemed to be the case and it gave examples of class A is augmented { ... }. However this didn’t work in Rakudo but eventually I came across is also which did.

I like the look of class A is also { ... }. However Moritz on IRC #perl6 mentioned that the Perl 6 spec had changed so my example would need to be:

augment class Ninja {    
    method battle_cry {
        say $.name ~ ' says zing!!!'; 
    }
}

Rakudo is currently a bit behind Perl 6 spec here but above will replace is also shortly. The change to augment makes sense because it avoids any confusion with roles in the class declaration.

The second bump was how to create a method dynamically. Now being familiar with Moose I had expected the following to work:

Ninja.meta.add_method( 'swing', method ( Str $sound_effect ) { 
    say "{$.name}: {$sword_symbol} {$sound_effect}";
});

And according to most Perl 6 docs .meta was the method to access the metaclass (MOP). However meta produced a method not defined error

Trawling the web further I did find that you could do:

Ninja.swing = method { say "Changed to zing" };

But this only allowed you to redefine a method, not create a new one.

Luckily IRC #perl6 came to the rescue again! jnthn & Moritz pointed me to $object.^add_method( ... ) and the docs on the ng branch of Rakudo on Github.

Perl6 does have some beautiful syntax. I love the $drew does Throwstar line. Soon Rakudo will be able to do:

$drew does role {
    method throw_star { say "throwing star" }
};

So this, augment and probably lots more will be part of the ng branch which will be merged with the Rakudo master in the not too distant future.

/I3az/

I personally would describe that metaprogramming provides the ability to:

transform programs with programs

and leave it at that!

The article that stirred the metaprogramming pot was Metaprogramming: Ruby vs. Javascript. This actually is a good post and it helped fill in a few holes in my “fragile” Javascript knowledge.

Luckily I believe my Perl is a bit less fragile!, so I thought I would convert the metaprogramming examples into Perl & Moose.

So following the blogs examples, below defines the Ninja class in Moose. MooseX::SingletonMethod loads Moose with a bit of singleton method sugar.

use Modern::Perl;

{
    package Ninja;
    use MooseX::SingletonMethod;
    use namespace::clean -except => 'meta';
    
    has name => ( is => 'rw', isa => 'Str' );
}

my $drew = Ninja->new( name => 'Drew' );
my $adam = Ninja->new( name => 'Adam' );

Now we re-open the Ninja class and add battle_cry method like so:

{
    package Ninja;
    
    sub battle_cry {
        my $self = shift;
        say $self->name . ' says zing!!!'; 
    }
}

$drew->battle_cry;   # => Drew says zing!!!
$adam->battle_cry;   # => Adam says zing!!!

Now using MooseX::SingletonMethod we add throw_star singleton method into $drew object:

$drew->add_singleton_method( throw_star => sub {
    say "throwing star";
});

$drew->throw_star;   # => throwing a star

To call method dynamically we do this:

$drew->${ \'battle_cry' };   # => Drew says zing!!!

Create colour method closing over $colour_name (ie. closure):

my $colour_name = 'black';

Ninja->meta->add_method( colour => sub {
    my $self = shift;
    say "${ \$self->name }'s colour is $colour_name";
});

$drew->colour;    # => Drew's colour is black
$adam->colour;    # => Adam's colour is black

Finally… “defining a method dynamically on an instance that closes over local scope and accesses the instance’s state”

my $sword_symbol = '********';

$drew->add_singleton_method( swing => sub {
    my ($self, $sound_effect) = @_;
    say "${ \$self->name }: $sword_symbol $sound_effect";
});

$drew->swing( 'slash!!' );   # => Drew: ********* slash!!

Everything nicely works the same as the Ruby & Javascript blog examples.

To round things off, below is the complete example but with MooseX::Declare sugar stirred into the pot.

use Modern::Perl;
use MooseX::Declare;

class Ninja with MooseX::SingletonMethod::Role is mutable {
    has name => ( is => 'rw', isa => 'Str' );
}

my $drew = Ninja->new( name => 'Drew' );
my $adam = Ninja->new( name => 'Adam' );

###########################################################

class Ninja is mutable {    
    method battle_cry {
        say $self->name . ' says zing!!!'; 
    }
}

$drew->battle_cry;   # => Drew says zing!!!
$adam->battle_cry;   # => Adam says zing!!!

###########################################################

$drew->add_singleton_method( throw_star => sub {
    say "throwing star";
});

$drew->throw_star;   # => throwing a star

###########################################################

$drew->${ \'battle_cry' };   # => Drew says zing!!!

###########################################################

my $colour_name = 'black';

Ninja->meta->add_method( colour => sub {
    my $self = shift;
    say "${ \$self->name }'s colour is $colour_name";
});

$drew->colour;    # => Drew's colour is black
$adam->colour;    # => Adam's colour is black

###########################################################

my $sword_symbol = '********';

$drew->add_singleton_method( swing => sub {
    my ($self, $sound_effect) = @_;
    say "${ \$self->name }: $sword_symbol $sound_effect";
});

$drew->swing( 'slash!!' );   # => Drew: ********* slash!!

/I3az/

PS. If you want Moose in Javascript then have a look at Joose