[oak perl] Question: Scalar::Util::dualvar usage in general

[Mark Bole]

I've made a brief attempt to understand this item, after stumbling 
across it while looking up something else -- a typical short story of my 
professional life, I guess! ;-)

How is the Scalar::Util::dualvar subroutine implemented?  Yes, I've 
looked at the C source code in the ext/List/Util/Util.xs file...  but as 
soon as I saw variables with the string "magic" embedded in the name, I 
gave up.

The closest real-life example seems to be Perl built-in errors, in other 
words, using errno=2 as an example,

    % perl -de 0

    Loading DB routines from perl5db.pl version 1.19
    Editor support available.

    Enter h or `h h' for help, or `man perldebug' for more help.

    main::(-e:1):   0
      DB<1> $! = 2;

      DB<2> print $!;
    No such file or directory
      DB<3> print $!+0;
    2
      DB<4> print 'No such file or directory' + 0
    0


As a database-oriented person, I'm wondering if there are any other 
real-life examples for using this capability -- overloading a variable 
with both string and numeric datatypes...

Is there any situation where casting a scalar as "dualvar" would be 
preferable to simply creating a hash, with numbers as keys and 
corresponding strings as values?

-- 
Mark Bole
http://www.bincomputing.com
925-287-0366


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