First some definitions:
Factory
A class that generates instances of other classes, choosing which class to build on the basis of run-time information.
Façade
A class that acts as a front-end for one or more other classes, delegating the actual work to those classes as appropriate.

In your particular example, what you want is a factory: a class that generates objects according to where the sun rises. For example: 

# Rational helper class...

package Astro::Data::Scientific;

use base Solar::Data;
use base Lunar::Data;

# <define methods here>



# "Differently rational" helper class...

package Astro::Data::Mythological;

use base Astrological::Data;        # Pre-empt normal methods
use base Astro::Data::Scientific;

# <overload any methods here that the 
#  heavens dictate should behave differently>



# Factory class...

package Astro::Data;

# Constructor returns instances of helper classes,
# depending on run-time astro[nl]o[mg]ical conditions

sub new {
    shift; # off class name

    if ($sun_rises_in_west) {
        return Astro::Data::Mythological->new(@_);
    }
    else {
        return Astro::Data::Scientific->new(@_);
    }
}

# <no methods of its own, since it's never actually instantiated>

[download]

In reply to Re: Modification of @ISA at run time by TheDamian
in thread Modification of @ISA at run time by jkeenan1

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.