Re: Dumb, non-question: How to return 'nothing'.

[Anonymous Monk]

See Higher Order Perl, Chapter 4.5 THE SEMIPREDICATE PROBLEM

# array reference version
sub make_iterator {
    ... return Iterator {
        my $return_value;
        ...
          if (exhausted)
        {
            return;
        }
        else {
            return [$return_value];
        }
    }
}

[hardburn]

That's a nice solution, but is there any particular reason to use an arrayref rather than a scalarref? It'd make the iterating code just a bit cleaner:

while( my $next = $iter->() ) {
    $next = $$next;
    ...
}

As opposed to:

while( my $next = $iter->() ) {
    ($next) = @$next;
    ...
}

[BrowserUk]

I think I've settled on requiring that the iterator be called in a list context. Eg.:

sub i{ 
    my $n = shift; 
    return sub{ $n ? $n-- : () } 
};;

$i = i( 5 ); 
print $_ while ( $_ ) = $i->();;
5
4
3
2
1

[SuicideJunkie]

Would be worthwhile to add carp "Iterator not called in list context" unless wantarray; so it can't be used improperly?

[Anonymous Monk]

That's a nice solution, but is there any particular reason to use an arrayref rather than a scalarref?

Its copy/paste from the book, the first solution -- I guess its more generic, re-usability and all that :)

[ikegami]

Seeing as a scalar is always being returned,

while( my $next = $iter->() ) {
    ($next) = @$next;
    ...
}

can be shortened to

while( my ($next) = @{ $iter->() } ) {
    ...
}