Beefy Boxes and Bandwidth Generously Provided by pair Networks
more useful options
 
PerlMonks  

Re: autovivication and referencing

by sundialsvc4 (Abbot)
on Nov 20, 2013 at 14:11 UTC ( #1063532=note: print w/replies, xml ) Need Help??


in reply to autovivication and referencing

Also keep in mind that the first scenario specifies a reference to a variable, other_hash.   So, you now have two or more references to the same chunk of storage.   (Fortran calls that EQUIVALENCE.)

Data::Dumper makes this clear.   Consider this:

use strict; use warnings; use Data::Dumper; my @a = (1, 2); my $b = { "c"=>\@a }; print Dumper(\@a, $b); $b->{"c"}[0]=4; print Dumper(\@a, $b);'
(gives...)
$VAR1 = [ 1, 2 ]; $VAR2 = { 'c' => $VAR1 }; $VAR1 = [ 4, 2 ]; $VAR2 = { 'c' => $VAR1 };

The dumper knows that the hash-key points to the same block of storage that the array-variable does, so it refers to it in the second case by its name.   And you can see how a change, made by means of the hash-key, changed the value in the array variable, because the two are the same.   This is a very easy mistake to make in a production setting.

Also note that “references” will work in this way, whether-or-not a particular reference comes into existence by means of the “autovivification” feature.

Log In?
Username:
Password:

What's my password?
Create A New User
Node Status?
node history
Node Type: note [id://1063532]
help
Chatterbox?
[stevieb]: berrybrew has been updated with the new perl checksums. Now I'm going to implement dynamic loading of perls thanks to their new JSON releases file
[LanX]: GotToBTru ++ # erix & MySql ... talk about a database trigger xD

How do I use this? | Other CB clients
Other Users?
Others meditating upon the Monastery: (12)
As of 2017-03-30 16:01 GMT
Sections?
Information?
Find Nodes?
Leftovers?
    Voting Booth?
    Should Pluto Get Its Planethood Back?



    Results (360 votes). Check out past polls.