Re: fwp Digest 19 Oct 2004 13:50:49 -0000 Issue 310

Jason Foster <[email protected]> wrote:

This is probably not the place for these kind of questions, but here
goes anyway.

> Can anyone help me to understand why this code refuses to compile?                                      
> Even better, can anyone help fix it :)                                                                  
>                                                                                                         
>     %hash = qw( fred filntstone barney rubble tom delong );                                             
>     print( keys( reverse( %hash ) ) );                                                                  
>                                                                                                         
> The error message...                                                                                    
>                                                                                                         
>     Type of arg 1 to keys must be hash (not reverse) at ./killme.pl                                     
> line 4, near ") ) "                                                                                     
>                                                                                                         
> ... was pretty confusing since it implies that "reverse" is a type?!                                    

The implication was meant to just indicate what you were saying instead
of what perl was expecting. reverse is not a type :)

But the type of what reverse returns is a list, not a hash. I wondered
about this once too. Your attempt at a solution:

>     print( keys( %{ reverse( %hash ) } ) );                                                             

was almost right, but not quite. You can't dereference a list, but you
can deref a reference to an anonymous hash:

     print keys %{ { reverse %hash } };

Note, by the way, that if you know your data contains no duplicate
values, you could simply have done this:

     print values %hash;

-- 
Gaal Yahas <[email protected]>
http://gaal.livejournal.com/