Hello Mark,
On Fri, 27 Nov 2009 19:48:09 -0800 (PST)
Mark_Galeck <[email protected]> wrote:
> Hello, the following question I posted on perl.beginners but for a few
> days there is no response, so maybe it is not a beginners question?
> Nah, it must be :)
This question bounces on some subtleties in Perl's references and
syntax.
> --------------------------------
> If I can do this:
>
> $ref = \...@foobar;
> print @$ref;
Yes.
> then why can't I do this:
>
> print @\...@foobar;
This appears to be a syntax error, probably having to do with the @\@
not parsing as you expect. If you re-write it as
print @{...@foobar};
is works as you probably intend. Unfortunately, I cannot imagine why
you would want to do that.
> ------------------------------------
> I have this kind of problem often, let me give another example, I
> think it is similar, let me know if not.
This is a completely different issue.
> Why are all the printouts different:
>
> @foobar = ();
> print \...@foobar; #prints as reference to ARRAY
As it should.
> $foobar = \();
> print $foobar; # prints as reference to SCALAR
Although many people misunderstand it, () does not create a list. The
parens only provide grouping. In this case, you are taking a reference
to a grouped nothing and perl is interpreting that as a request for
a reference to an undef scalar.
> print \(); #prints as array of references to SCALAR, in this case
> empty array
Correct.
I would definitely suggest spending quality time with perlref and
perlreftut. They will help you work through the syntactic oddities in
references. There is a really good discussion of some of this at the
Perl Monastery (http://perlmonks.org/?node_id=779217)
Many people develop habits that reduce some of the confusion. I only
derefence references in one of two ways (out of several).
* If I need the whole item, I use the sigil and curlies. I never use
just the derefencing sigil.
@{$foo} not @$foo
It reads better to me and is less prone to the kinds of syntax attack
you had above.
* If I need an element of a referenced array or hash, I use the arrow
notation.
$foo->{'a'} not ${$foo}{'a'}
I find that the arrow helps me later in reading the code. The visual
reminder of the reference simplifies my own code reading.
I would definitely suggest you check out the Perl Monastery. It is
a great community for helping with questions like this.
G. Wade
--
Against logic there is no armor like ignorance. -- Laurence J. Peter
