Path: utzoo!utgpu!jarvis.csri.toronto.edu!clyde.concordia.ca!uunet!bfmny0!tneff
From: tneff@bfmny0.UU.NET (Tom Neff)
Newsgroups: comp.lang.perl
Subject: Re: Passing scalars by reference
Message-ID: <15235@bfmny0.UU.NET>
Date: 6 Mar 90 20:45:12 GMT
References: <1220@frankland-river.aaii.oz.au> <7293@jpl-devvax.JPL.NASA.GOV>
Reply-To: tneff@bfmny0.UU.NET (Tom Neff)
Lines: 48

In article <7293@jpl-devvax.JPL.NASA.GOV> lwall@jpl-devvax.JPL.NASA.GOV (Larry Wall) writes:
>	3) Use the type glob *name to pass in the symbol name: ...
>
>This last method is the most powerful, because you can pass anything that has
>a name in the symbol table, including filehandles, subroutines and formats.
>What you're really doing is passing in the symbol table entry for everything
>with that name and giving it a new name locally.

Also note something not covered explicitly in the manual:  This is the
only way you can pass multiple arrays to a subroutine without effectively
concatenating them into one amorphous array.

For example if I want to be able to say

	@Questions = ("who", "what", "why");
	@Answers = ("us", "this", "because");
	@Weights = ("40", "35", "25");

	$score = &process_one_quiz($pupil, @Questions, @Answers, @Weights);

I cannot just say

	sub process_one_quiz {
		local ($p, @Q, @A, @W) = @_;
		...
	}

because @Q eats the rest of the @_ array including answers and weights.
(The parameter list is ONE list.)  But if I say

	sub process_one_quiz {
		local ($p, *Q, *A, *W) = @_;
		for $i ($[..$#Q) {
			print "$Q[$i],$A[$i],$W[$i]\n";
			# (real work deleted)
		}
	}

	$score = &process_one_quiz($pupil, *Questions, *Answers, *Weights);

then everything works right.

Thus pass-by-reference can be an important tool for passing arrays even
when the subroutine has no need to modify any elements.  (Larry might
want to mention this in the manual.)
-- 
To have a horror of the bourgeois   (\(    Tom Neff
is bourgeois. -- Jules Renard        )\)   tneff@bfmny0.UU.NET