... vast majority of the time, the caller is going to want that value in plain old string format.... sometimes they want both string and special formats from the same call ...

How about just use good old wantarray to either: 

c:\@Work\Perl\monks>perl -wMstrict -MData::Dump -le
"sub flexi {
   my ($str) = @_;
   ;;
   my ($string, $special) = map { uc, scalar reverse } $str;
   ;;
   return wantarray ? (string => $string, special => $special)
                    : $string
                    ;
   }
 ;;
 my %hash = flexi('foobar');
 dd \%hash;
 ;;
 my $string = flexi('foobar');
 dd $string;
"
{ special => "raboof", string => "FOOBAR" }

"FOOBAR"

[download]
or: 
c:\@Work\Perl\monks>perl -wMstrict -MData::Dump -le
"sub flexi {
   my ($str) = @_;
   ;;
   my ($string, $special) = map { uc, scalar reverse } $str;
   ;;
   return wantarray ? ($string, $special)
                    : $string
                    ;
   }
 ;;
 my $string1 = flexi('foobar');
 dd $string1;
 ;;
 my ($string2, $special) = flexi('foobar');
 dd $string2, $special;
"
"FOOBAR"

("FOOBAR", "raboof")

[download]

Give a man a fish:  <%-{-{-{-<

In reply to Re^5: OO design: returning string and/or special value by AnomalousMonk
in thread OO design: returning string and/or special value by wanna_code_perl

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.