Re: nonempty false list

A hash slice in a scalar context returns the last element. @x{1, 2} equals (2, undef) and so undef is used as the boolean.

The second one constructs a new array, and therefore the array count is returned in a scalar context, 2.

%x = (1 => 2);

print '@x{1, 2} in scalar equals: \'' . (scalar @x{1, 2}) . "'\n";
# Returns ''

print '@{[@x{1, 2}]} in scalar equals: \'' . (scalar @{[@x{1, 2}]})) .
+ "'\n";
# Returns 2
[download]

Comment on Re: nonempty false list Download Code

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Re^2: nonempty false list by Anonymous Monk on Mar 10, 2011 at 18:47 UTC
Hmm thanks to everyone, I definitely see the distinction. What I am TRYING to do is this: I have a hash, and I want to test whether any of three separate keys produce a 'true' value. So, it looks something like this (I boiled it down for the first example) `if(@opts{qw\|a b c\|}) { }` [download] Which seemed pretty elegant, but as previously discussed does not work, because its a hash slice. THIS, however, seems horribly inelegant: `if(@{[@opts{qw\|a b c\|}]}) { }` [download] But perl must have something better than this: `if($opts{a} \|\| $opts{b} \|\| $opts{c}) { }` [download]	[reply] [d/l] [select]
Re^3: nonempty false list by kennethk (Abbot) on Mar 10, 2011 at 18:52 UTC
Testing each value of a list sounds like a job for grep. When I need to determine if any elements of a list are true, I will usually use something that looks like: `if( grep $_, @opts{qw\|a b c\|}) { }` [download] A cleaner version of this would be `if( grep $opts{$_}, qw\|a b c\|) { }` [download] You can use a couple negations to check if all values are true: `if( !grep !$opts{$_}, qw\|a b c\|) { }` [download] Note that your second suggestion will always return true, since you will always have a 3-element array in scalar context.	[reply] [d/l] [select]
Re^3: nonempty false list by wind (Priest) on Mar 10, 2011 at 18:59 UTC
Just use grep `if (grep {$opt{$_}} qw(a b c)}) {` [download] And you can even capture the keys for which true is returned `if (my @keys = grep {$opt{$_}} qw(a b c)}) { print "@keys match\n";` [download]	[reply] [d/l] [select]
Re^3: nonempty false list by ikegami (Patriarch) on Mar 10, 2011 at 19:06 UTC
There's also List::MoreUtils's `any`. `any { $_ } @opts{qw( a b c )}` [download]	[reply] [d/l] [select]