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POHow can I provide an alternate init arg for an attribute in Moose?
 

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  1. POHow can I provide an alternate init arg for an attribute in Moose?
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    <p>I of course know that I can rename the init arg for an attribute by setting <code>init_arg</code> (e.g) </p> <pre><code>package Test { use Moose; has attr =&gt; ( is =&gt; 'ro', isa =&gt; 'Str', init_arg =&gt; 'attribute' ); } </code></pre> <p>which would allow me to</p> <pre><code>Test-&gt;new({ attribute =&gt; 'foo' }); </code></pre> <p>but not</p> <pre><code>Test-&gt;new({ attr =&gt; 'foo' }); </code></pre> <p>at the same time</p> <p><a href="https://metacpan.org/module/MooseX%3a%3aAliases" rel="nofollow">MooseX::Aliases</a> actually has this behavior, but creating an alias also creates accessors. I'm currently trying to understand the code in that module to see if I can't determine how it does it, so that I can replicate said functionality (in a way I understand). If someone could explain how to do it here with an example that'd be great.</p> <p><em>update</em> it appears that MX::Aliases is doing this by way of replacing what's actually passed to the constructor in an <code>around initialize_instance_slot</code> but I'm still not sure how that's actually getting called, because in my test code my around isn't actually getting executed.</p> <p><em>update</em> munging in <code>BUILDARGS</code> isn't really an option because what I'm trying to do allow setting of the accessor via the name of the <em>label</em> I'm adding to the attribute via <a href="https://metacpan.org/module/Moose%3a%3aCookbook%3a%3aMeta%3a%3aRecipe3" rel="nofollow">Meta Recipe3</a>. You might say I'm doing</p> <pre><code>has attr =&gt; ( is =&gt; 'ro', isa =&gt; 'Str', alt_init_arg =&gt; 'attribute' ); </code></pre> <p><em>update</em></p> <p>here's what I've managed to work out with what I'm trying to do so far.</p> <pre><code>use 5.014; use warnings; package MooseX::Meta::Attribute::Trait::OtherName { use Moose::Role; use Carp; has other_name =&gt; ( isa =&gt; 'Str', predicate =&gt; 'has_other_name', required =&gt; 1, is =&gt; 'ro', ); around initialize_instance_slot =&gt; sub { my $orig = shift; my $self = shift; my ( $meta_instance, $instance, $params ) = @_; confess 'actually calling this code'; return $self-&gt;$orig(@_) unless $self-&gt;has_other_name &amp;&amp; $self-&gt;has_init_arg; if ( $self-&gt;has_other_name ) { $params-&gt;{ $self-&gt;init_arg } = delete $params-&gt;{ $self-&gt;other_name }; } }; } package Moose::Meta::Attribute::Custom::Trait::OtherName { sub register_implementation { 'MooseX::Meta::Attribute::Trait::OtherName' } } package Message { use Moose; # use MooseX::StrictConstructor; has attr =&gt; ( traits =&gt; [ 'OtherName' ], is =&gt; 'ro', isa =&gt; 'Str', other_name =&gt; 'Attr', ); __PACKAGE__-&gt;meta-&gt;make_immutable; } package Client { use Moose; sub serialize { my ( $self, $message ) = @_; confess 'no message' unless defined $message; my %h; foreach my $attr ( $message-&gt;meta-&gt;get_all_attributes ) { if ( $attr-&gt;does('MooseX::Meta::Attribute::Trait::OtherName') &amp;&amp; $attr-&gt;has_other_name ) { $h{$attr-&gt;other_name} = $attr-&gt;get_value( $message ); } } return \%h; } __PACKAGE__-&gt;meta-&gt;make_immutable; } my $message = Message-&gt;new( Attr =&gt; 'foo' ); my $ua = Client-&gt;new; my %h = %{ $ua-&gt;serialize( $message )}; use Data::Dumper::Concise; say Dumper \%h </code></pre> <p>problem is that my <code>around</code> block is never being run and I'm not sure why, maybe I'm wrapping it in the wrong place or something.</p>
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    1. COCould you give some examples of the desired behaviour? From what you describe, BUILDARGS mangling would do exactly the right things... That is: what readers/writers do you want for this attribute? What init_args?
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    2. COan example of desired behavior is very close to what MooseX::Aliases actually does. But I haven't figured out what all it has to do to do it. Also it uses an array, and I don't want/need that. basically buildargs seems good when I need to do it once, but it's not really per attribute, it's per class. I want something per attribute.
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    3. COyou can apply MooseX::Aliases on a per-attribute basis.
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