| Tie::CPHash(3pm) | User Contributed Perl Documentation | Tie::CPHash(3pm) |
Tie::CPHash - Case preserving but case insensitive hash table
This document describes version 2.000 of Tie::CPHash, released January 17, 2015.
use Tie::CPHash 2; # allows initialization during tie
tie %cphash, 'Tie::CPHash', key => 'value';
$cphash{'Hello World'} = 'Hi there!';
printf("The key `%s' was used to store `%s'.\n",
tied(%cphash)->key('HELLO WORLD'),
$cphash{'HELLO world'});
The Tie::CPHash module provides a hash table that is case preserving but case insensitive. This means that
$cphash{KEY} $cphash{key}
$cphash{Key} $cphash{keY}
all refer to the same entry. Also, the hash remembers which form of the key was last used to store the entry. The "keys" and "each" functions will return the key that was used to set the value.
An example should make this clear:
tie %h, 'Tie::CPHash', Hello => 'World';
print $h{HELLO}; # Prints 'World'
print keys(%h); # Prints 'Hello'
$h{HELLO} = 'WORLD';
print $h{hello}; # Prints 'WORLD'
print keys(%h); # Prints 'HELLO'
Tie::CPHash version 2.000 introduced the ability to pass a list of "key => value" pairs to initialize the hash (along with the "add" method that powers it). The list must include a value for each key, or the constructor will croak.
The additional "key" method lets you fetch the case of a specific key:
# When run after the previous example, this prints 'HELLO':
print tied(%h)->key('Hello');
(The "tied" function returns the object that %h is tied to.)
If you need a case insensitive hash, but don't need to preserve case, just use $hash{lc $key} instead of $hash{$key}. This has a lot less overhead than Tie::CPHash.
"use Tie::CPHash;" does not export anything into your namespace.
tied(%h)->add( key => value, ... ); tied(%h)->add( \@list_of_key_value_pairs );
This method (introduced in version 2.000) adds keys and values to the hash. It's just like
%h = @list_of_key_value_pairs;
except that it doesn't clear the hash first. It accepts either a list or an arrayref. It croaks if the list has an odd number of entries. It returns the tied hash object.
If the list contains duplicate keys, the last "key => value" pair in the list wins. (You can't pass a hashref to "add" because it would be ambiguous which key would win if two keys differed only in case.)
For people used to Tie::IxHash, "add" is aliased to both "Push" and "Unshift". (Tie::CPHash does not preserve the order of keys.)
$set_using_key = tied(%h)->key( $key )
This method lets you fetch the case of a specific key. For example:
$h{HELLO} = 'World';
print tied(%h)->key('Hello'); # prints HELLO
If the key does not exist in the hash, it returns "undef".
Tie::CPHash requires no configuration files or environment variables.
None reported.
No bugs have been reported.
Christopher J. Madsen "<perl AT cjmweb.net>"
Please report any bugs or feature requests to "<bug-Tie-CPHash AT rt.cpan.org>" or through the web interface at <http://rt.cpan.org/Public/Bug/Report.html?Queue=Tie-CPHash>.
You can follow or contribute to Tie-CPHash's development at <https://github.com/madsen/tie-cphash>.
This software is copyright (c) 2015 by Christopher J. Madsen.
This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.
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| 2015-01-17 | perl v5.20.2 |