Re: "Did not find leading dereferencer" - new findings to an old puzzle

Peter J. Holzer schrieb:
The use Switch was in the code only for historic reason, and I have
removed it. I don't know of course if *this* was sufficient to make
the error go away: After all, the removal of the statement made the
code a little bit smaller, so the problem might simply have
disappeared for *this* reason (removing a comment line instead of the
use Switch would have had the same effect).

Possible, but unlikely. Unless you use another module which uses
Text::Balanced, you aren't calling Text::Balanced any more and hence
can't get any error messages from it any more.

Well, you are free to get a copy of my code to see what I'm using.
Aside from the Switch, I'm using:

use Carp qw(croak cluck confess);
use File::Temp qw(mktemp);
use File::Basename;

I have no idea whether these modules use Text::Balanced, but note that
even
when I do a "use Switch", I never actually *write* a switch statement.

Then I have the impression that the error message "comes from the
Switch module
and goes away when I remove it". I think this does not describe the
situation. If at
all, we can say that the Switch module somehow *masks* the real
error/warning
message. This means: I *do* have some construct which normally would
yield an
error (or warning) message, but instead I get the "leading
dereferencer" error; and
when I simplify the program (for example, by only removing a single
comment line
out of a set of other comment lines, in a completely different part of
the program),
the "leading dereferencer" error disappears and instead I see the
*real* error (or
warning) message.

If you can explain this behaviour just by the fact that I have a "use
Switch" at
the beginning, without ever using a switch, I am curious to know how
you do it...

I don't think it has anything to do with the size. The problem was
probably that the Switch module needs to parse the source code and that
uses a different grammar than perl (which is unavoidable, as the purpose
of Switch is to change the grammar). So changing a character which
shouldn't make a difference in Perl does make a difference in
Perl+Switch.

I've had a look at Switch.pm .... this module doesn't even have a BEGIN
section.
It definitely does not need to parse the source code of the whole
program.
Instead it works by passing around code blocks when a switch
"statement"
is actually used in my program.

Then I've checked Text::Balanced. Looks similarly harmless (nothing be
done
unless you actually *use* some of its features). The only *probably*
suspicious
line is an overloading of the string conversion, i.e.

use overload '""' => sub { "$_[0]->{error}, detected at offset
$_[0]->{pos}" };

and the "leading dereferencer" is triggered when on code analysis, a
variable
name was expected and the leading "$" or "@" or "%" was not found.
Still I didn't
see anything which might cause this error to pop up when none of the
features
in the "use" module are never actually called.

In addition, I would like to point out that I had the same error
message a few
months ago in a different context. Following a recommendation in this
newsgroup,
I found in that case that it helped to remove the prototype declaration
from a
function definition, and the problem disappeared (i.e. I got the "real"
error message
displayed again, instead of the "dereferencer" one).

There is one point in which I agree with you: The error message is
likely related
to the fact that Text::Balanced is somehow included in the compilation
- after
all, that message is defined there and the Perl compiler is unlikely to
invent
this wording on its own. But I don't believe that this is due to a bug
in Text::Balanced.
At least to me, it is very hard to imagine that a bug in a module,
which is only
"use"'d, but never "used" (pun intended), could turn a very valid error
message at
a completely different point in the source code, into a "Leading
Dereferencer"
one, unless we also assume a bug in the Perl compiler itself. This
would require
- if it is possible at all, which I doubt - such a deep "introspection"
in its own code,
that one would find a trace of it by glancing over the source code of
Balanced.

Ronald

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