Re: [MacPerl-AnyPerl] using DATA for testing

[Chris Nandor <pudge@pobox.com>]

Copied to the list, for they may be interested in this little known feature
in Perl.

At 14:52 -0400 1999.08.11, Paul Corr wrote:
>	*INPUT = *DATA{GLOB};
>
>I understand these are typeglobs but where does 'GLOB' come from? Is
>it some sort of reserved word like DATA? Is this in a POD somewhere?
>I see STDIN, STDOUT, and STDERR in perlop.pod (and numerous books.)
>DATA I picked up in my list reading. Is it documented somewhere?

I am not sure where it is documented, but it is known.

Basically, every typeglob (like *FOO) has several parts to it, which may or
may not be filled.  The array part of a typeglob is called ARRAY, the
scalar is called SCALAR, and so on.  For instance, to get the SCALAR value
of *FOO, you can do:

  @FOO = (0..2);  $FOO = 3;
  *BAR = *FOO;

Now @BAR is the same as @FOO and $BAR is the same as $FOO.  But you can do
this, too:

  *BAR = \$FOO;

That will make $BAR an alias to $FOO as before, but not affect @BAR at all.
Then, you can do:

  *BAR = *FOO{SCALAR};

which is the same thing.  I like it because it looks more like I am
aliasing something.

I actually made a mistake above, though.  GLOB should have been IO or
FiLEHANDLE (they are both the same thing).  GLOB is just a pointer to the
typeglob itself.  So this is best:

  *INPUT = *DATA{IO};

That's the only way I can think of to get an alias to the filehandle.  As
noted before, you can do these:

  *BAR = \$FOO;
  *BAR = \@FOO;
  *BAR = \%FOO;

But there is no similar notation for filehandles.  So if you don't want to do:

  *BAR = *FOO;

to get the filehandle, you can do:

  *BAR = *FOO{IO};

-- 
Chris Nandor          mailto:pudge@pobox.com         http://pudge.net/
%PGPKey = ('B76E72AD', [1024, '0824090B CE73CA10  1FF77F13 8180B6B6'])

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