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POMoose (Perl): convert undef to empty string or 0 rather than die()
 

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    <p>I've received <strong>a lot of exceptions</strong> from QA due to incomplete data being fed to my Moose constructors. The attribute name is present in the constructor arguments, but the value is <code>undef</code>.</p> <p>It's a fact of life with many scripting applications that things are just <code>undef</code>. And oftentimes this is perfectly fine. You don't want an annoying warning from the <code>warnings</code> pragma (so you do <code>no warnings 'uninitialized'</code>), and you certainly don't want your code to die because one little value, say the housenumber, is <code>undef</code>.</p> <p>So without further ado, I want my Moose constructors to behave like straight Perl (i.e. without <code>use warnings 'uninitialized'</code>), which is to convert <code>undef</code> to <code>0</code> or the empty string as required. The attempt shown in this sample does not work for the case where the attribute name is present but the value is <code>undef</code>. I could think of using <code>BUILDARGS</code> to achieve what I want. But is there a declarative way in plain Moose without <a href="https://stackoverflow.com/q/5823685/269126">resorting to MooseX::UndefTolerant</a> (which unfortunately I cannot use as it is not installed)? </p> <pre><code>package AAA; use Moose; has 'hu', is =&gt; 'ro', isa =&gt; 'Str'; has 'ba', is =&gt; 'ro', isa =&gt; 'Int'; no Moose; __PACKAGE__-&gt;meta-&gt;make_immutable; package BBB; use Moose; extends 'AAA'; has '+hu', default =&gt; ''; # don't want to die on undef has '+ba', default =&gt; 0; # idem no Moose; __PACKAGE__-&gt;meta-&gt;make_immutable; package main; use Test::More; use Test::Exception; # Those AAAs should die ... throws_ok { AAA-&gt;new( hu =&gt; undef ) } qr/Validation failed for 'Str' with value undef/; throws_ok { AAA-&gt;new( ba =&gt; undef ) } qr/Validation failed for 'Int' with value undef/; # .. but these BBBs should live: lives_ok { BBB-&gt;new( hu =&gt; undef ) } 'hu supplied as undef'; lives_ok { BBB-&gt;new( ba =&gt; undef ) } 'ba supplied as undef'; done_testing; </code></pre>
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    1. COAs far as I know, you shouldn't be trying to suppress warnings. Why don't you check if values are defined before hand? `(defined($value))` Also, you could install `MooseX::UndefTolerant` locally to some directory `$my_dir` and `use lib($my_dir);`
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    2. COThe problem is type constraints. When you say foo isa Int, and you supply an undef for foo, it fails the type constraint because undef isn't an Int.
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    3. CO@YGomez +1 Nice idea, I might in fact be doing this. :-) As for warnings because of uninitialized values, see [`common::sense`](http://p3rl.org/common::sense). I agree with the author Marc Lehmann in his discussion of uninitialized values. (There are exceptions, but hey - they're exceptions.) Checking the values beforehand is just cumbersome. I'd have to repeat the checks in many places and I try to stay [DRY](http://en.wikipedia.org/wiki/Don%27t_repeat_yourself).
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