Yes, I should have clarified that it is a runtime error, but it is not a silent error. Thank you for bringing that up.

You understand perlguts far better than I, but there is a measurable penalty for interacting with a hash with locked keys: 

#!/usr/bin/perl
use strict;
use warnings;

use 5.10.0;

use Hash::Util 'lock_keys';
use Benchmark 'cmpthese';

lock_keys my %hash1, qw/foo bar baz/;
my %hash2;

cmpthese(1e2, {
    'lock'      => sub { for (1 .. 1e5) {$hash1{foo}++;$hash1{bar}++;$
+hash1{baz}++;} },
    'no_lock'   => sub { for (1 .. 1e5) {$hash2{foo}++;$hash2{bar}++;$
+hash2{baz}++;} },
});

[download]
yields 
          Rate    lock no_lock
lock    61.6/s      --     -8%
no_lock 66.8/s      8%      --

[download]

#11929 First ask yourself `How would I do this without a computer?' Then have the computer do it the same way.

In reply to Re^3: strict "vars" mode for hash key literals? by kennethk
in thread strict "vars" mode for hash key literals? by perlancar

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