Beefy Boxes and Bandwidth Generously Provided by pair Networks
P is for Practical
 
PerlMonks  

defined() might be a good idea

by BronzeWing (Monk)
on Aug 17, 2002 at 20:09 UTC ( #190914=note: print w/replies, xml ) Need Help??


in reply to Re: Re: Check on if statement
in thread Check on if statement

I think defined() is a good idea if there's a possibility of $foo being undefined, so as to avoid a warning about an undef being used in a string comparison/regex. Assuming an undefined value counts as a blank, I would write it like this:

if (!defined($foo) or $foo =~ m/^\??$/) { # Foo is valid }

Thus: "If foo is undefined, or matches an empty string or a single question mark."

But wasn't there something about \n's counting as "^" and/or "$"? Hmmm...


The Secret to Fortune Cookies in One Line
print join("... in bed", `fortune fortunes` =~ m/^(.*)(\.|\?|\!)$/), "\n";

Replies are listed 'Best First'.
Re: defined() might be a good idea
by BrowserUk (Patriarch) on Aug 17, 2002 at 21:16 UTC

    I wasn't saying that defined() doesn't have important uses, only that it use as given in the referenced post was not useful.

    That said, I wouldn't use a regex as you have either. You point out one reason yourself, though m//s would probably address that concern, but, as others pointed out earlier, using a regex to test a string against a single, predefined char (or word)--especially when that char is a non-word char, meaning that the m//i option would be of no benefit--is simply overkill.

    Personally, I would probably code the test as:

    if ( !defined($foo) or $foo eq '' or $foo eq '?' ) { print "\$foo OK!\n"; }

    as using a regex against a fixed string seems pointless and I prefer positive conditions to negative ones.

    Update:Modified condition, struck irrelevant comments. Seems I lost track of the original questioners reqs. Personally, I probably still wouldn't use a regex for this.


    What's this about a "crooked mitre"? I'm good at woodwork!
      I havent read the rest of the thread, I only comment because of your mistake in the cb ;-), but the test you describe:
      if ( defined($foo) and $foo eq '?' ) { print "\$foo OK!\n"; }
      Would be better (Lazier) written
      print "\$foo OK!\n" if $foo and $foo eq '?';
      in my opinion anyway...

      Note that since $foo must be a '?', then it cant be _any_ false value, defined being only one of three. Thus you can dispose of the defined test and replace it with simple true or false.

      Yves / DeMerphq
      ---
      Software Engineering is Programming when you can't. -- E. W. Dijkstra (RIP)

Log In?
Username:
Password:

What's my password?
Create A New User
Domain Nodelet?
Node Status?
node history
Node Type: note [id://190914]
help
Chatterbox?
and the web crawler heard nothing...

How do I use this? | Other CB clients
Other Users?
Others perusing the Monastery: (4)
As of 2023-01-30 07:18 GMT
Sections?
Information?
Find Nodes?
Leftovers?
    Voting Booth?

    No recent polls found

    Notices?