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=head1 TITLE
Index Attribute
=head1 VERSION
Maintainer: David Nicol <[EMAIL PROTECTED]>
Date: 19 Sep 2000
Mailing List: [EMAIL PROTECTED]
Number: 262
Version: 1
Status: Developing
=head1 ABSTRACT
An attribute C<:n> is defined which means the index or key of a
contained item. This attribute is useful when an index number is needed
within a C<foreach> statement, it also may be used inside container-like
abstractions
which dynamicly generate their contents.
=head1 DESCRIPTION
foreach $item (@items){
#print "$item was at location ",$item:n,"\n";
print "$item was at location ${item:n}\n";
};
Given acceptance of several other iffy proposals,
@Nplus1 = lazy sub { return $_:1 + 1 }; # or something like this
=head1 DISCUSSION
When this was suggested on the language-objects list,
there was discussion of the name of the attribute, with C< :i > being
suggested as well as C< :index >
We also need access to attributes of variables as a standard language
feature, that is implicit here.
Another possibility would be to use C< $[ > for the attribute, which
makes sense if we allow C< $[ > to be set individually per container.
Use of brackets in variable names is a Big Hassle for parsing:
print "$item was at location ${item:[}\n";
is parseable if colon is elevated to the same level of immediacy,
in terms of eating subsequent tokens, as dollar-sign now has.
Use of left-bracket as the index attribute matches very well with
the situation of pulling sequential items out of a function pretending
to be a list, though, as internal to the code
we can refer to $[, "The index of the first item", to get the index
of the current item after several items have been shifted off (and
the specific $[ attribute incremented each time.)
@Nplus1 = lazy sub { return $[ + 1 }; # or something like this
=head1 IMPLEMENTATION
Within looping constructs, we only need to track this if it is used.
We may be using an implied c-like C<for> when we do a looping construct
anyway, in which case we already have the information, and just need some
Perl syntax for sharing it with user code. In linked-list kinds of
situations, we will need to identify the need to track this info and
then track it for the user.
In terms of $[ we would make the familiar and vaguely deprecable $[ be
the global to which the one specific to an array instance defaults to
or starts at. (which may deserve it's own RFC it is true.)
=head1 REFERENCES
John McNamara left this radical suggestion out of RFC 120.
