Try this one for size: 

use strict;
use warnings;
use Hash::Util qw( lock_keys unlock_keys );

my %hash = ( 'name' => "Doraemon", 
             'age'  => "1000"
           );

lock_keys( %hash );

# oh! my birthday, i'm getting older
$hash{'ege'} = "1001";  # oops, just TRIED to add new key.

[download]

...and the output... 

Attempt to access disallowed key 'ege' in a restricted hash at 
C:\Perl\scripts\hashtest.pl line 14.

[download]

Enjoy!


Dave

In reply to Re: hash, a troublemaker? by davido
in thread hash, a troublemaker? by Doraemon

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.