RFC 206 (v2) Arrays: @#arr for getting the dimensions of an array

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=head1 TITLE

Arrays: @#arr for getting the dimensions of an array

=head1 VERSION

  Maintainer: Buddha Buck <bmbuck@14850.com>
  Date: 8 Sep 2000
  Last Modified: 19 Sep 2000
  Mailing List: perl6-language-data@perl.org
  Number: 206
  Version: 2
  Status: Frozen

=head1 ABSTRACT

This RFC proposes the use of the @# prefix to get the bounds and
dimensionality of a multidimensional array.

=head1 DESCRIPTION

The $#array notation is useful for getting the upper bound of a
unidimensional array, but is not as useful for getting the upper bounds of
a multidimensional array. A multidimensional array should have a list of
upper bounds, not a single upper bound.

This RFC proposes using @#array, analogous to $#array, to get the list of
upper bounds for a multidimensional array @array. The length of @#array
would indicate the dimensionality of @array.

=head2 Example

   sub printbounds (\@) {
     my $arrayref = shift;
     my $array = @$arrayref;
     print "D:", scalar @#arrayref," B:(",join(',',@#arrayref),")\n";
   }

   my int @a :bounds(2,2,2,2,2);
   printbounds(@a); # "D:5 B:(2,2,2,2,2)\n"

   my int @b :bounds(@a); # create @b the same size as @a
   printbounds(@b); # "D:5 B:(2,2,2,2,2)\n"

   my @c = (1,2,3,4,5,6,7,8,9,10);
   printbounds(@c); # "D:1 B:(9)\n"

=head1 IMPLEMENTATION

Presumably, multidimensional arrays would have to store their bounds
somewhere to have the semantics provided in RFC 203. This operator would
simply return to the user those stored bounds.

Where an array is declared without ':bounds', @# returns the largest
bounds of each dimension that has been accessed:

   my int @d = ();
   $d[[3,4]] = 5;
   @e = @#d;        # (3,4)

=head1 REFERENCES

RFC 203: Notation for declaring and creating arrays

• RFC 206 (v2) Arrays: @#arr for getting the dimensions of an array by Perl6 RFC Librarian