Beefy Boxes and Bandwidth Generously Provided by pair Networks
Syntactic Confectionery Delight
 
PerlMonks  

Why does passing a subroutine an undefined element in a hash create it?

by faq_monk (Initiate)
on Oct 08, 1999 at 00:20 UTC ( #634=perlfaq nodetype: print w/replies, xml ) Need Help??

Current Perl documentation can be found at perldoc.perl.org.

Here is our local, out-dated (pre-5.6) version:

If you say something like:

    somefunc($hash{"nonesuch key here"});

Then that element ``autovivifies''; that is, it springs into existence whether you store something there or not. That's because functions get scalars passed in by reference. If somefunc() modifies $_[0], it has to be ready to write it back into the caller's version.

This has been fixed as of perl5.004.

Normally, merely accessing a key's value for a nonexistent key does not cause that key to be forever there. This is different than awk's behavior.

Log In?
Username:
Password:

What's my password?
Create A New User
Chatterbox?
[stevieb]: I have learned that my daughter has significant brain injury, so that's affecting my decisions. Don't know who to reach out to. I just want to vent. I am honestly lost. It's something I can't code around.
[stevieb]: I am infuriated at the same time I am hopeless. It appears there are approaches to 'fix' things, but, you know..,

How do I use this? | Other CB clients
Other Users?
Others drinking their drinks and smoking their pipes about the Monastery: (5)
As of 2017-02-25 04:05 GMT
Sections?
Information?
Find Nodes?
Leftovers?
    Voting Booth?
    Before electricity was invented, what was the Electric Eel called?






    Results (365 votes). Check out past polls.