You could also just create class Z, subclassing Y, which has a Z::A with your special stuff. Then create your objects of Z instead of Y on the condition. 
BEGIN { package X; sub A {} sub B {} }
BEGIN { package Y; @ISA=qw(X); sub B {} }
BEGIN { package Z; @ISA=qw(Y); sub A {} }

my $object = ($opt{specialcase} ? 'Z' : 'Y')->new(@newargs);

[download]

-- Randal L. Schwartz, Perl hacker

update: I added the BEGIN above. Too asleep when I hacked before to remember that. {grin}

In reply to Re: Best Method of Object-Oriented Behavior Addition? by merlyn
in thread Best Method of Object-Oriented Behavior Addition? by princepawn

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.