Re: [coldsync-hackers] Ok, what am I doing wrong???

[Izzy Blacklock <izzyb at ecn dot ab.ca>]

On June 12, 2003 10:05 am, Andrew Arensburger wrote:
> On Tue, 10 Jun 2003, Izzy Blacklock wrote:
> > I'm trying to pass two arrays to a function like this:
> >
> >         # Run the dump function the user specified.
> >         $DumpFunction{$HEADERS{'Target'}}->(\@NamesArray, \@parsedData );
> >
> > My function works when I do it this way:
> >
> > sub textDump
> >         {
> >         my ( $names, $data) = @_;
> >         foreach ( @$data )
> >                 {
> >
> >
> > But I have no need for $names in this target function, so I'd like to do
> > something like this:
> >
> > sub textDump
> >         {
> > 	shift;
> >         foreach ( @$_ )
> >                 {
> >
> > This doesn't work as I expected.  My understanding of shift is that it
> > should take the first value off the list (in this case \@NamesArray) and
> > return it (in this case drop it), leaving the rest of the list. 
> > Shouldn't that leave $_ = \@parsedData?
>
> 	No. Within a function, 'shift' modifies @_, not $_. Those are two
> separate variables. @_ is an array, and $_ is a scalar. Yes, Perl allows
> you to have the same name for a scalar, an array, a hash, ...
> 	What you want is not $_, but the first element of @_, so use
>
> 	foreach (@{$_[0]})

Oh, I understand now (I think).  So to do what I was trying to do above, I 
should be able to so this:

 sub textDump
         {
 	shift;		# Drop Ref-to-arry of names; not needed
	my $data = shift;
         foreach ( @$data )
                 {

> 	Just in passing: as a matter of style, I prefer to declare 'my'
> variables at the top of a function, rather than using @_ directly. So I'd
> write &textDump as:
>
> 	sub textDump
> 	{
> 		my $names = shift;	# Ref-to-array of names. Ignored
> 		my $data = shift;	# Ref-to-array of data.
> 		my $foo;		# Some other variable used later
>
> 		foreach my $item (@{$data})
> 		{
> 			...
>
> I find that a block of "= shift"s helps to clarify what arguments the
> function expects. YMMV. HTH.

I like the  my ( $names, $data) = @_; approach myself.  Probably because it 
reminds me of the way you define parameter names in C functions. :)  

...Izzy
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