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copied!<p>There are of course a lot of ways to combine a bunch of values into a more complex value -- that's basically what the study of data structures is about. What particular data structures to choose is a fairly involved question, highly dependent on your actual use cases.</p> <p>I know fairly little about your case, but the thing I've gleaned from your question that all of these attributes represent similarly-structured concepts. And so I would create a new data type, the <code>Scale</code>:</p> <pre><code>use MooseX::Declare; class Scale { for (qw/min max def/) { has $_ => (is => 'ro', isa => 'Num', required => 1); } has val => (is => 'rw', isa => 'Num', lazy_build => 1); method _build_val() { return $self->def; } method BUILD($args) { confess "Out of range!" unless $self->_is_in_range($self->val); } method _is_in_range($val) { return defined $val && $val >= $self->min && $val <= $self->max; } before val ($new_val?) { return unless defined $new_val; confess "Out of range!" unless $self->_is_in_range($new_val); } } </code></pre> <p>And I would present attributes on some <code>ThingWithScale</code> that were backed by a <code>Scale</code> object.</p> <pre><code>class ThingWithScale { has _attr => ( is => 'ro', isa => 'Scale', default => sub { shift->_make_attr() }, ); method _make_attr($class: $val?) { return Scale->new( min => 100, max => 1000, def => 200, (defined $val ? (val => $val) : ()), ) } # Convert `attr` argument to a `Scale` object before passing to real constructor. sub BUILDARGS { my ($class, %args) = @_; if (defined (my $attr = delete $args{attr})) { %args = ( %args, _attr => $class->_make_attr($attr) ); } return $class->SUPER::BUILDARGS(%args); } } my $thing = ThingWithScale->new(attr => 101); </code></pre> <p>And about the time I was writing that <code>BUILDARGS</code> method to automatically instantiate a Scale object from the simple constructor parameter, I would realize that what I really wanted to do was to invent a new attribute <a href="http://search.cpan.org/~ether/Moose-2.0900-TRIAL/lib/Moose/Manual/Attributes.pod#Attribute_traits_and_metaclasses" rel="nofollow">trait</a> to describe attributes that had minimum and maximum legal values.</p>

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