I wonder, how to prevent (control) hashes members?
Let say

my %hash;       
$hash{'name'} = "Doraemon";
$hash{'age'} = "1000";

#... some code
# oh! my birthday, i'm getting older
$hash{'ege'} = "1001";   # oops, i just add new key
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How to avoid this (silly) mistake?
One way i can think of is to define the keys in constants,

$k_name = 'name';
$k_age = 'age';

$hash{$k_ege} = "Do";   # warning, gotcha!
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so the compiler can catch the mistake, when use strict. Any more 'efficient' ideas?