Tie::Hash::KeysMask                                           version   0.01

- Control key aliasing by mask function, e.g. omit case of character
- distinction

        use Tie::Hash::KeysMask;

        my $mask = sub {...};
        tie %argH, 'Tie::Hash::KeyMask',$mask, more arguments;

         Yield that the key mask function &$mask translates any key
         when applied to %argH like ..

                $k   =>   $mask->($k, more arguments)

         that is

                 $argH{$k}  expands to  $argH{$mask->($k, more arguments)}
            $argH{$k} = $v  expands to  $argH{$mask->($k, more arguments)} = $v

    If e.g. choose key mask "sub {uc $_[0]}" one can access an element
    without care of case of the key. In place of "sub { }" particular items
    can be used which will be translated into a CODE. The translation is

                'lc' => sub { lc $_[0] }
                'uc' => sub { uc $_[0] }
                \%M  => sub { exists $M{$_[0]} ? $M{$_[0]} : $_[0]}

    A class-method "codemap" manage this translation. If it is pleased one
    could override it and add ones own translations.

    This class inherits from "Tie::Hash::Create" by which the tied hash can
    be obtained anonymously as reference with the command

                'Tie::Hash::KeyMask'->newHASH (sub {...}, more arguments)

    which overrides the tie syntax calling tie from body of newHash.

    Tie::Hash::Create, Sub::ParamFrame.

    The mask function must satisfy this rule: Each of different keys which
    are considered as equal must be mapped to one and the same value only.
    Hence, if \&mask is given as agument of the construtor, no triple of
    different keys $a,$b,$c such that $b = mask($a) and $c = mask($b) are
    admitted. It's ease to receive counter examples which break this rule
    using certain hashs for mask in order to observe funny results.

    This module requires these other modules and libraries:

    Josef Schönbrunner <j.schoenbrunner@onemail.at>

    Copyright (c) 2005 by Josef Schönbrunner This library is free software;
    you can redistribute it and/or modify it under the same terms as Perl
    itself, either Perl version 5.8.7 or, at your option, any later version
    of Perl 5 you may have available.