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=begin React :component<HeaderCol> :id<menu> 
=para L<Documentation|/doc/introduction>
=para L<Modules| /mods>
=para L<Examples| file:../examples/index.podlite>
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=para L<About|file:../about/index.podlite>
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README

use v6.c;

module Attribute::Predicate:ver<0.0.3>:auth<zef:lizmat> {
    multi sub trait_mod:<is>(Attribute:D \attr, :$predicate!) is export {
        if $predicate {
            my $name := $predicate ~~ Bool
              ?? "has-{attr.name.substr(2)}"
              !! $predicate.Str;
            my $method := method { attr.get_value(self).defined }
            $method.set_name($name);
            attr.package.^add_method($name,$method)
        }
    }
}



Attribute::Predicate - add "is predicate" trait to Attributes


class Foo {
    has $.bar is predicate;         # adds method "has-bar"
    has $.baz is predicate<bazzy>;  # adds method "bazzy"
}


Foo.new(bar => 42).has-bar;    # True
Foo.new(bar => 42).bazzy;      # False


This module adds a C<is predicate> trait to C<Attributes>.  It is similar
in function to the "predicate" option of Perl's C<Moo> and C<Moose> object
systems.


If specified without any additional information, it will create a method
with the name "has-{attribute.name}".  If a specific string is specified,
then it will create the method with that given name.


The method in question will return a C<Bool> indicating whether the attribute
has a defined value.


Source can be located at: https://github.com/lizmat/Attribute-Predicate .
Comments and Pull Requests are welcome.


This library is free software; you can redistribute it and/or modify it under the Artistic License 2.0.


Predicate

Attribute::Lazy - lazy attribute initialisation


=begin code

use Attribute::Lazy;

class Foo {
    has $.foo will lazy { "zub" };
    has $.booble will lazy { $_.bungle };
    method bungle() {
        'beep';
    }

}

=end code


This is based on an experimental trait that was briefly in the Rakudo core.


Attribute::Lazy provides a single C<trait> C<will lazy> that will allow
an attribute with a public accessor (that is one defined with the C<.> twigil,)
to be initialised I<the first time it is accessed> by the result of the supplied
block.  This might be useful if the value may not be used and may be expensive
to calculate (or various other reasons that haven't been thought of.)


The supplied block will have the object instance passed to it as an argument,
which can be used to call other methods or public accessors on the object, you
probably want to avoid calling anything that may depend on the value of the
attribute for obvious reasons.



module Attribute::Lazy {

    my role Builder[Callable $block] {
            method compose(Mu $package) {
                callsame;
                my $attr = self;
                if $attr.has_accessor {
                    my $meth-name = self.name.substr(2);
                    $package.^method_table{$meth-name}.wrap(-> $self {
                        if not $attr.get_value($self).defined {
                            $attr.set_value($self, $block($self));
                        }
                        callsame;
                    });
                }
            }

    }

    multi sub trait_mod:<will>(Attribute:D $attr, Callable $block, :$lazy!) is export(:DEFAULT) {
        $attr does Builder[$block];
    }

}


# vim: expandtab shiftwidth=4 ft=raku


Lazy

The Raku Knowledge Base


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=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|#>
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    =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>

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    =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


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README

Attribute::Lazy

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Attribute::Lazy v0.0.6

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