Re: Truthfulness of references

return_ref, as its name announces, returns a reference to a hash. That reference gets assigned to a scalar variable ($ref) as is fine an proper. A rather bogus test for "truth" is then made to see if $_ is a reference to anything (is that what you thought the test actually was?).

I'm not sure what issue you are trying to illustrate, however the following code may provide a little illumination:

use strict;
use warnings;

my $scalar = 'a string is a scalar';

print ref ({}), "\n";
print ref ([]), "\n";
print ref (ret_hash ()), "\n";
print ref (ret_array ()), "\n";
print ">", ref ($scalar), "<\n";
print ref (\$scalar), "\n";

sub ret_hash {my %hash; return \%hash;}
sub ret_array {my @array; return \@array;}
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Prints:

HASH
ARRAY
HASH
ARRAY
><
SCALAR
[download]

ref tells you something about the type of reference you point it at (but nothing about scalars). ref on it's own tells you about whatever reference $_ contains (which is the test you were making in your if).

DWIM is Perl's answer to Gödel

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Re^2: Truthfulness of references by njcodewarrior (Pilgrim) on Mar 13, 2007 at 11:08 UTC
Thanks GrandFather. That's what I thought the test was actually doing So what's a good way to test for truth here? The reason for the post is that I've written a few subroutines that either return a reference to a complex data structure OR filter entries out of the previously created data structure. The problem I noticed was that if I ended up filtering out all of the entries and returning a reference to the filtered data structure, my test for truth returned unexpected results ( ie: it returned true eventhough the data structure was empty. 3 follow up questions: 1. Should I be returning references from these types of sub-routines? 2. If so, what's the best way to return them? 3. What's a good way to test for truthfulness: `if ( %$ref ) { ...do something }` [download] or... `if ( %$ref && ref $ref eq 'HASH' ) { ...do something }` [download] Thanks again for your help. njcodewarrior	[reply] [d/l] [select]
Re^3: Truthfulness of references by Anno (Deacon) on Mar 13, 2007 at 13:11 UTC
You wrote: 3. What's a good way to test for truthfulness: "Truthfulness" is an unusual term for the boolean value of something. "Truth value" is more common. `if ( %$ref ) { ...do something }` [download] That code is fine if you know that `$ref` holds a hash ref and you need to decide whether the hash is empty. or... `if ( %$ref && ref $ref eq 'HASH' ) { ...do something }` [download] Here, it seems, you want to check whether the reference you have is indeed a hash ref, but put this way the condition is pretty much useless. Since you try a hash dereference first, if the ref isn't a hash ref your code will die before it gets to the test. You'd have to swap the parts for them to make sense: `if ( ref $ref eq 'HASH' && %$ref ) {` [download] Anno	[reply] [d/l] [select]