The London Perl and Raku Workshop takes place on 26th Oct 2024. If your company depends on Perl, please consider sponsoring and/or attending.


Tie::Hash::KeysMask - 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: Tie::Hash::Create


Josef Schönbrunner <>


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.