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POPerl: fixing Moose attribute and type coercion problems
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  1. POPerl: fixing Moose attribute and type coercion problems
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    copied!<p>I recently upgraded Moose to v1.15 and found that a set of modules I use no longer worked. The error I get is:</p> <pre><code>You cannot coerce an attribute (source) unless its type (GOBO::Node) has a coercion at /opt/local/lib/perl5/site_perl/5.12.0/darwin-multi-2level/Moose/Meta/Role/Application/ToClass.pm line 142 </code></pre> <p>I can see several possible sources of error and would be grateful for advice on how to fix the problem.</p> <p>The first bit of code for GOBO::Node looks like this:</p> <pre><code>package GOBO::Node; [...] extends 'GOBO::Base'; with 'GOBO::Labeled'; with 'GOBO::Attributed'; coerce 'GOBO::Node' =&gt; from 'Str' =&gt; via { new GOBO::Node(id=&gt;$_) }; has 'source' =&gt; (is =&gt; 'rw', isa =&gt; 'GOBO::Node'); </code></pre> <p>The roles used by this package also have attributes that are GOBO::Nodes, and the attribute 'source' mentioned in the error message is one of them.</p> <ul> <li><p>part of the reason for having the coercion in GOBO::Node seems to be as a shortcut when creating a new node. Would it be better to use BUILDARGS rather than coerce?</p></li> <li><p>where should I put the coercion if I want several packages to be able to use it? If I add the coercion to (e.g.) GOBO::Attributed, I get a warning that it already exists. Without the coercion, though, I get the warning above about not being able to coerce.</p></li> <li><p>there is a separate package of subtypes; would it be better to create a subtype of GOBO::Node--e.g. GOBO::Node::ProtoNode--and a coercion, and use that for the attributes should be GOBO::Nodes?</p></li> </ul> <p>Thank you for any help or advice on this problem!</p>
 

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