CHANGELOG

head

item

root

para

L<Examples| file:../examples/index.podlite>


L<Download |file:../download/index.podlite>


React

=begin React :component<HeaderCol> :id<menu> 
=para L<Documentation|/doc/introduction>
=para L<Modules| /mods>
=para L<Examples| file:../examples/index.podlite>
=para L<Download |file:../download/index.podlite>
=para L<About|file:../about/index.podlite>
=para 🔍 K<⌘K>/K<ctrl-K>
=end React


HEADER

FOOTER

ChangeLog

code

Mooish

C<AttrX::Mooish> - extend attributes with ideas from Moo/Moose (laziness!)


use AttrX::Mooish;
class Foo {
    has $.bar1 is mooish(:lazy, :clearer, :predicate) is rw;
    has $!bar2 is mooish(:lazy, :clearer, :predicate, :trigger);
    has Num $.bar3 is rw is mooish(:lazy, :filter);


method build-bar1 {
    "lazy init value"
}


method !build-bar2 {
    "this is private mana!"
}


method !trigger-bar2 ( $value ) {
    # do something after attribute changed.
}


method filter-bar3 ( $value, *%params ) {
    if %params<old-value>:exists {
        # Only allow the value to grow
        return ( !%params<old-value>.defined || $value > %params<old-value> ) ?? $value !! %params<old-value>;
    }
    # Only allow inital values from 0.5 and higher
    return $value < 0.5 ?? Nil !! $value;
}


method baz {
    # Yes, works with private too! Isn't it magical? ;)
    "Take a look at the magic: «{ $!bar2 }»";
}
}


say $foo.bar1;
say $foo.bar3.defined ?? "DEF" !! "UNDEF";
for 1..10 { $foo.bar3 = rand; say $foo.bar3 }


The above would generate a output similar to the following:


lazy init value
UNDEF
0.08662089602505263
0.49049512098324255
0.49049512098324255
0.5983833081770437
0.9367804461546302
0.9367804461546302
0.9367804461546302
0.9367804461546302
0.9367804461546302
0.9367804461546302


This module is aiming at providing some functionality we're all missing from Moo/Moose. It implements laziness,
accompanying methods and adds attribute value filter on top of what standard Moo/Moose provide.


What makes this module different from previous versions one could find in the Raku modules repository is that it
implements true laziness allowing I<Nil> to be a first-class value of a lazy attribute. In other words, if you look at
the L<#SYNOPSIS> section, C<$.bar3> value could randomly be either undefined or 3.1415926.


This section is inteded for beginners and could be skipped by experienced lazybones.


As always, more information could be found by Google. In few simple words: a lazy attribute is the one which gets its
first value on demand, i.e. – on first read operation. Consider the following code:


class Foo {
    has $.bar is mooish(:lazy, :predicate);


my $foo = Foo.new
say $foo.has-bar; # False
say $foo.bar;     # 3.1415926...
say $foo.has-bar; # True


Laziness becomes very handy in cases where intializing an attribute is very expensive operation yet it is not certain
if attribute is gonna be used later or not. For example, imagine a monitoring code which raises an alert when a failure
is detected:


class Monitor {
    has $.notifier;
    has $!failed-object;


submethod BUILD {
    $!notifier = Notifier.new;
}


method report-failure {
    $.notifier.alert( :$!failed-object );
}


Now, imagine that notifier is a memory-consuming object, which is capable of sending notification over different kinds
of media (SMTP, SMS, messengers, etc...). Besides, preparing handlers for all those media takes time. Yet, failures are
rare and we may need the object, say, once in 10000 times. So, here is the solution:


class Monitor {
    has $.notifier is mooish(:lazy);
    has $!failed-object;


method build-notifier { Notifier.new( :$!failed-object ) }


method report-failure {
    $.notifier.alert;
}


Now, it would only be created when we really need it.


Such approach also works well in interactive code where many wuch objects are created only the moment a user action
requires them. This way overall responsiveness of a program could be significally incresed so that instead of waiting
long once a user would experience many short delays which sometimes are even hard to impossible to be aware of.


Laziness has another interesting application in the area of taking care of attribute dependency. Say, C<$.bar1> value
depend on C<$.bar2>, which, in turn, depends either on C<$.bar3> or C<$.bar4>. In this case instead of manually defining
the order of initialization in a C<BUILD> submethod, we just have the following code in our attribute builders:


method build-bar2 {
    if $some-condition {
        return self.prepare( $.bar3 );
    }
    self.prepare( $.bar4 );
}


This module would take care of the rest.


The L<#SYNOPSIS> is a very good example of how to use the trait C<mooish>.


For all the trait parameters, if it is applied to a private attribute then all auto-generated methods will be private
too.


The call-back style options such as C<builder>, C<trigger>, C<filter> are expected to share the privace mode of their
respective attribute:


=begin code
    class Foo {
        has $!bar is rw is mooish(:lazy, :clearer<reset-bar>, :predicate, :filter<wrap-filter>);

        method !build-bar { "a private value" }
        method baz {
            if self!has-bar {
                self!reset-bar;
            }
        }
        method !wrap-filter ( $value, :$attribute ) {
            "filtered $attribute: ($value)"
        }
    }
=end code


Though if a callback option is defined with method name instead of C<Bool> I<True> then if method wit the same privacy
mode is not found then opposite mode would be tried before failing:


=begin code
    class Foo {
        has $.bar is mooish( :trigger<on_change> );
        has $!baz is mooish( :trigger<on_change> );
        has $!fubar is mooish( :lazy<set-fubar> );

        method !on_change ( $val ) { say "changed! ({$val})"; }
        method set-baz { $!baz = "new pvt" }
        method use-fubar { $!fubar }
    }

    $inst = Foo.new;
    $inst.bar = "new";  # changed! (new)
    $inst.set-baz;      # changed! (new pvt)
    $inst.use-fubar;    # Dies with "No such private method '!set-fubar' for invocant of type 'Foo'" message
=end code


The Raku Knowledge Base


=begin React :component<HeaderCol> :id<footer>  
=begin nested :!nested
=item1 B<Language>
    =item2 L<Get started|file:../getting-started/getting-started.podlite>
    =item2 L<Why Raku?|/doc/language/faq#Why-should-I-learn-Raku-What's-so-great-about-it>
    =item2 L<Try Raku|https://glot.io/new/raku>
    =item2 L<Raku cheat sheet|https://github.com/Raku/mu/blob/master/docs/Perl6/Cheatsheet/cheatsheet.txt>
    =item2 L<empty|#>
    =item2 L<empty|#>
    =item2 L<empty|#>
    =item2 L<Raku on Exercism|https://exercism.org/tracks/raku>
    =item2 L<Wikipedia|https://en.wikipedia.org/wiki/Raku_(programming_language)>
    =item2 L<empty|#>
    =item2 L<empty|#>
    =item2 L<empty|#>

=end nested
=begin nested :!nested

=item1 B<L<Documentation|/doc>>
    =item2 L<Getting started, Migration guides from other languages, & Tutorials | file:../doc/introduction.podlite>
    =item2 L<Language References|file:../doc/reference.podlite>
    =item2 L<Type Reference| file:../doc/types.podlite>
    =item2 L<Miscellaneous| file:../doc/miscellaneous.podlite>
    =item2 L<FAQs (Frequently Asked Questions)|/doc/language/faq>
    =item2 L<Community|/doc/language/community>
    =item2 L<The list of all documents|file:../doc/index.podlite>

=item1 B<Resources>
    =item2 L<The Raku Guide|https://raku.guide/>
    =item2 L<Books |https://perl6book.com/>
    =item2 L<Rosetta Code | https://www.raku.org/community/rosettacode>

=end nested
=begin nested :!nested

=item1 B<Resoures>
    =item2 L<Download | file:../download/index.podlite>
    =item2 L<empty|#>
    =item2 L<empty|#>
    =item2 L<empty|#>
    =item2 L<empty|#>
    =item2 L<empty|#>
    =item2 L<empty|#>
    =item2 L<empty|#>

=item1 B<Learning>
    =item2 L<The Raku Guide|https://raku.guide/>
    =item2 L<Wikibook |https://en.wikibooks.org/wiki/Raku_Programming>
    =item2 L<Books |https://perl6book.com/>
    =item2 L<Rosetta Code | https://www.raku.org/community/rosettacode>
    =item2 L<Learn Raku in Y minutes|https://learnxinyminutes.com/docs/raku/>
    =item2 L<Golfing |https://github.com/AlexDaniel/raku-golf-cheatsheet>
=end nested
=begin nested :!nested

=item1 B<Explore>
    =item2 L<Raku Blog Aggregator|https://planet.raku.org/>
    =item2 L<Rakudo Weekly|https://rakudoweekly.blog/>
    =item2 L<The Weekly Challenge |https://perlweeklychallenge.org/>
    =item2 L<Raku Advent Calendar|https://raku-advent.blog/>
    =item2 L<empty|#>
    =item2 L<empty|#>
    =item2 L<empty|#>
    =item2 L<empty|#>
    =item2 L<empty|#>

=end nested
=end React


=begin React :component<CookieConsent> :id<CookieConsent> :buttonCaption("Got it!")
=para
This website uses cookies for analytics.
=end React


ChangeLog

CHANGELOG

v0.7.4

AttrX::Mooish v0.7.4

Authors

License

Dependencies

Test Dependencies

Provides

Documentation