testing defined($x) && length($x)

perl5ever has asked for the wisdom of the Perl Monks concerning the following question:

Replies are listed 'Best First'.
Re: testing defined($x) && length($x) by ikegami (Patriarch) on Mar 25, 2009 at 15:45 UTC
Sure: `if (has_length($x)) { ... }` [download] Implementation of `has_length` left to the reader.	[reply] [d/l] [select]
Re: testing defined($x) && length($x) by kyle (Abbot) on Mar 25, 2009 at 15:53 UTC
Building on the remarks from Bloodnok and ikegami, I think this does what you're asking: `if ( length( $x // '' ) {` [download] Update: Oops, kennethk has informed me that I missed an important part of the question. Maybe this is better, but maybe not: `if ( length( defined $x ? $x : '' ) ) {` [download]	[reply] [d/l] [select]
Re: testing defined($x) && length($x) by ruzam (Curate) on Mar 25, 2009 at 17:20 UTC
When I do need to worry about '0', I generally stick with `if (defined $x and $x ne '')` Now I'm wondering if there's any particular advantage of using "`length($x)`" over "`$x ne ''`"? If $x is a sub parameter and both '0' and 'undef' are acceptable input, then I sanitize it right up front so I don't have to worry about undefined warnings later in the code when I start using/testing with it. `my $x = shift; $x = '' unless defined $x;` [download]	[reply] [d/l] [select]
Re: testing defined($x) && length($x) by Bloodnok (Vicar) on Mar 25, 2009 at 15:46 UTC
Given that the test will fail if either `$x` is undefined or is defined but is empty, you could avoid the uninitialized value... warning by using `if (length($x \|\| '')) { ... }` [download] A user level that continues to overstate my experience :-))	[reply] [d/l] [select]
Re^2: testing defined($x) && length($x) by ikegami (Patriarch) on Mar 25, 2009 at 15:50 UTC
That introduces a false negative. The if's body is no longer executed when $x eq '0'.	[reply]
Re: testing defined($x) && length($x) by Herkum (Parson) on Mar 25, 2009 at 16:26 UTC
Why are you not just doing this? `if ($x and length($x)) {} # Do something` [download] This should take care of your $x not being defined. Update: Too early did not think clearly see below. Removed the offending/incorrect text.	[reply] [d/l]
Re^2: testing defined($x) && length($x) by kennethk (Abbot) on Mar 25, 2009 at 16:34 UTC
No, it still has the '0' false negative: `$ perl -e '$x = 0; print "failed\n" unless $x and length($x)' failed $` [download] vs. `$ perl -e '$x=0; $ print "failed\n" unless defined $x and length($x)' $` [download]	[reply] [d/l] [select]
Re^2: testing defined($x) && length($x) by Bloodnok (Vicar) on Mar 25, 2009 at 16:41 UTC
...length test will catch it if the value of $x = 0, hmmm, if `$x == 0`, then `length()` test will not be executed - aka, it suffers from the same problem (with my attempt) that ikegami kindly pointed out. A user level that continues to overstate my experience :-))	[reply] [d/l] [select]
Re: testing defined($x) && length($x) by JavaFan (Canon) on Mar 26, 2009 at 01:04 UTC
The more concise way is to not write `use warnings;` to begin with, and then: `if(''ne$x) {...}` [download]	[reply] [d/l] [select]