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Re: RFC 204 (v2) Arrays: Use list reference for multidimensional array access

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Buddha Buck
September 25, 2000 15:51
Re: RFC 204 (v2) Arrays: Use list reference for multidimensional array access
Message ID:
> On Fri, 22 Sep 2000 08:58:10 +1100, Jeremy Howard wrote:
> >Bart Lateur wrote:
> >> Hmm... the problem is, I think, that array references and ordinary
> >> scalars are both scalars.
> >>
> >That's true, but they're scalars with different interfaces. In particular,
> >an array ref can be dereferenced and provides an array in doing so. If an
> >index can do this, then it's a multidimensional index.
> That worries me. I'd like to avoid to repeat the fiasco of having the
> same code have different kinds of behavious, depending on the contents
> of a variable, as we have with symbolic references versus anonymous
> arrays/hashes.
> What will this return?
> 	$ary[$index]
> It looks like a plain and simple array item, but what if $index is an
> array ref?

Then it returns a plain and simple array item from a multidimensional 

The main problem I see are these:

@array = ([1,2],[3,4]);  # 2-dimensional array, using LOL syntax
print $array[[1,1]];     # prints 4, OK
print $array[1];         # prints ?????
print $array[[1,1,1]];   # prints ?????
print $array[[1]];       # prints ?????

According to RFC 204, $array[1] should return [3,4], $array[[1]] should 
return (3,4), and $array[[1,1,1]] should cause a runtime error.

Interestingly enough, my original version of RFC204 had all three of 
the "questionable" print statements be runtime errors -- I don't like 
LOL-semantics for multidimensional arrays.  Somehow, it got changed 
when being passed from me through Jerry to the RFC Librarian.  I didn't 
bother to reread it after it got posted -- I knew what it said -- so I 
didn't notice the change.

If anyone is interested, I'll post my original .pod I wrote...

> >> What would be the difference between
> >>
> >> $a[2]
> >>
> >> and
> >>
> >> $a[[2]]
> >>
> >> anyway? Aren't these just the same?
> >>
> >Nearly! From the RFC:
> >
> ><quote>
> >When a listref is used to index a list of lists, the returned list reference
> >is automatically dereferenced:
> >
> >  my @array( [0,1], [1,2]);
> >  my @a = @array[[0]]; # Returns (0,1), _not_ [0,1]
> ></quote>

That's part of what I didn't write in "my" RFC.

I especially don't like the line

    $array[[1,2]] = (1,2,3,4); # Sets the line at (1,2) to (1,2,3,4)

Huh?  That's a scalar on the right, a list on the left?  Should that 
set $array[[1,2]] to 4?

That'll teach me to proofread what "I" say....

> Puh. I'd prefer
> 	my @a = @$array[0];
> which is shorter anyway.   ;-)  Currently, this does the wrong thing,
> and I think that maybe the prefix precedence should be fixed so that
> 	@$ary[0]
> is the same as
> 	@{$ary[0]}
> Or doe people find it intuitive that this returns a slice of an array
> pointed to by $ary?

I'd find 

	my @a = @array[0;]; 

to be nicer -- no references visible, unambiguous, same number of 
characters as @$array[0], and symmetrical with

	my @b = @array[;0];

for a different dimension.  It isn't easy to do that with LOL notation.

> You are right in that. You cannot get a hash slice of a Perl4 style
> "multidimensional" hash. A major stumbling block.

A fatal one, in my opinion.

> -- 
> 	Bart.

     Buddha Buck                   
"Just as the strength of the Internet is chaos, so the strength of our
liberty depends upon the chaos and cacophony of the unfettered speech
the First Amendment protects."  -- A.L.A. v. U.S. Dept. of Justice

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