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POHow do I disable autovivification in Perl?
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copied!<p>Suppose you have a HUGE application "develoopped" ;) by a big team. Here is a simplified model of the potential disaster that may occur when somebody checks too deep in a data structure. If not possible to disable autovification completely or in scope, how to work around this? Thank you very much :) !!!!</p> <pre><code>use strict; use warnings;use Data::Dumper; my $some_ref = {akey=>{deeper=>1}}; print Dumper($some_ref ); if($some_ref->{deep}{doot} == 1){ print 'too deep '.$/; } if($some_ref->{deep}){ print 'Already in a deep doot'.$/; } print Dumper($some_ref ); </code></pre> <p>This outputs the following:</p> <pre><code>$VAR1 = { 'akey' => { 'deeper' => 1 } }; Use of uninitialized value in numeric eq (==) at autovivify_test.pl line 5. Already in a deep doot $VAR1 = { 'deep' => {}, 'akey' => { 'deeper' => 1 } }; </code></pre> <p>Yes I know there is a warning, but... it may be too late.</p> <p>Hey guys it will may be help to say that my hashref references a tied HASH.</p> <p>May be if I implement a good FETCH method which checks for checks deeper in the structure, I will solve easily my problem?</p> <hr> <p>I looked at <a href="http://search.cpan.org/~kvail/Tie-StrictHash-1.0/StrictHash.pm" rel="noreferrer">Tie::StrictHash</a>,<a href="http://perldoc.perl.org/5.8.8/Tie/Hash.html" rel="noreferrer">Tie::Hash</a> and <a href="http://perldoc.perl.org/perltie.html#Tying-Hashes" rel="noreferrer">perltie</a>. Here is simplified version of my solution:</p> <pre><code>#!/usr/bin/env perl; #test_tie.pl package StrictHash; use strict; use warnings; use Tie::Hash; our @ISA = qw(Tie::StdHash); use Carp; sub TIEHASH { my $class = shift; my $hash = bless {@_}, $class; return $hash; } ##======================================================================== ## FETCH fails if applied to a member that doesn't exist. ##======================================================================== sub FETCH { my ($hash, $key) = @_; Carp::confess "key '$key' does not exist" unless exists $hash->{$key}; return $hash->{$key}; } ##======================================================================== package main; use strict;use warnings;use Data::Dumper; #Imagine StrictHash is in ./StrictHash.pm #use StrictHash; my %hash; tie %hash, 'StrictHash', akey => {deeper=>1} ; my $some_ref =\%hash; print Dumper($some_ref ); if($some_ref->{deep}{doot} == 1){ print 'too deep '.$/; } </code></pre> <p>What I achieved is to touch only one place in the app. Now all Places like if($some_ref->{deep}{doot}) will cause die with stack-trace. So I will easily find them and correct them. And new writings of this kind will NOT be possible. Perl is good for big apps too, you just need to know more ;).</p> <p>Thank you all! I hope this helps others too.</p>

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