Getting to variables contained in a typeglob referenced by a scalar.

From: ddtl (this.is_at_invalid)
Date: 06/30/04 

Date: Wed, 30 Jun 2004 19:31:10 +0200

Hello,

After 'open' is called in the following way:

open my $fh, $file;

'$fh' contains a reference to a filehandle, i.e., somewhere in the 'open'
function there is probably a following assignment:

$fh = \*SOME_TYPEGLOB;

(and somehow that typeglob is anonymous (?), so the filehandle is
also anonymous).

If I understand correctly, it actually means that '$fh' contains
a reference to a typeglob, because wherever there is a filehandle,
it can be substituted for a typeglob.

Than, if we want to get to the variables inside that typeglob, we
have to do it in the following way:

*$fh - access the fileglob
*$fh->{SCALAR} - access a reference to a scalar (typeglob is also a special
                hash)
${*$fh->{SCALAR}} - access the scalar itself.

But "Programming Perl" (14.4.1) mentions another, easier way -
just use $$$fh (or @$$fh or %$$fh, etc.).

I don't understand, though, how it works - what do we access when
$$fh is used - there is no scalar reference inside '$fh'?
The book doesn't mention it as some new way of using typeglobs/references,
which probably means that it should be clear from the previous chapters
why and how it works, and it seems that I missed the point.

The question is, then: how and why $$$fh etc. work, and where is an
explanation for it in the book (or just in the documentation)

ddtl.

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