Good point, I started using the 'values' handler to grab a list of the values and shouldn't/won't be accessing the whole hash directly anyway.

I set the contents in the class by passing in $self->_industries( \%selected ); but from then on using the trait handles.

My previous implementations would have just stored the values in an array-ref, the move to using a hash is so I have quicker lookup with the ID of the values.

My hash looks like this btw, incase it makes a difference...

$obj->_industries( { 17 => { id => 17, name => 'foo' },
                     26 => { id => 26, name => 'bar' },
                   }
                 );
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There is obviously a duplication of the IDs, but that's minimal, and keeps the code that uses it simpler, rather than having to carry the ID AND the object around.

That's the only down-side I can think of.

btw, is the use of auto_deref no longer recommended in general, or only with Traits?

I use it everywhere else with basic ArrayRef[] types.

It is pretty much no longer recommended anywhere because it (ab)uses context and returns array/hash ref in scalar context and an array/hash in list context. While this is actually a fairly common idiom in Perl which I myself am long guilty of (ab)using (heck I even wrote the original auto-def code), it really is evil and should be stopped. The problem is that Perl context sensitivity can easily be the source of annoying and difficult to spot bugs, like for instance ...

# normal usage, works just fine ...
my @foo = $obj->foo; 
my $foo = $obj->foo; 

# but ...
$other_obj->bar( foos => $obj->foo ); # whoops!

# should actually be the more ugly ...
$other_obj->bar( foos => scalar $obj->foo );
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While it might seem trivial, it really can be difficult to track down sometimes, especially when this is your primary accessor. But of course, it is nice to not have to manually de-ref all the time (Perl 5.13++) which is pretty much why the Hash trait and Array trait both have an 'elements' to delegate to that returns the derefed item in a non-context sensitive way.
-stvn

Thankfully I've actually started to move to drop 'wantarray' at the end of my subs for those very reasons.

I think I'm much happier for a list to always be returned as a list, rather than, as you say, bizarre behaviour at times.