This and other RFCs are available on the web at
http://dev.perl.org/rfc/
=head1 TITLE
Formats out of core / New format syntax
=head1 VERSION
Maintainer: Nathan Wiger [EMAIL PROTECTED]
Date: 30 Aug 2000
Mailing List: [EMAIL PROTECTED]
Version: 1
Number: 181
Status: Developing
=head1 ABSTRACT
There has been much hinting at moving formats out of core. This RFC
proposes one way to do this, at the same time standardizing the syntax.
=head1 DESCRIPTION
=head2 Overview
Currently, the general consensus is that formats aren't widely used
enough to justify their living in the core binary. [1] However, they are
incredibly useful, and need to remain in the core distribution no matter
what.
Under this RFC, formats will be available through a simple:
use Format;
The rest of the RFC will address specific changes in syntax to make this
possible (and more consistent too).
=head2 Current Syntax
Currently, formats must be named for the bareword filehandle that
they're going to be used on, for example:
format FILE =
@: @
$name, $ssn
.
open FILE, "$file";
write FILE;
Some behind the scenes magic is done to bind these two together. In
order to change the format name, you have to use the following
statements:
$old = select FILE;
$~ = MYCUSTOMFORMAT;
select $old;
Getting this syntax to work as a module would be a collosal headache. In
addition, it's pretty peculiar to begin with. As such, a new but very
similar syntax is proposed.
=head2 New Syntax
Under the new syntax, a format will be held in a variable of the
Cformat type:
my format $FILE_FORMAT = q(
@: @
$name, $ssn
);
Note that declaring the format is remarkably similar to the current
form. However, it now can be handled with the existing variable syntax,
simplifying implementation. [2]
Using formats, however, requires one extra step, since there is no
longer any intrinsic property tying formats and filehandles together:
open $FILE, "$file";
format $FILE ($FILE_FORMAT); # $FILE-format($FILE_FORMAT)
write $FILE; # $FILE-write
Note, however, that this does get rid of the need to do all the special
Cselect statements. The Cformat and Cwrite methods could simply be
member functions of the C$FILE object.
However, I don't particularly like extra steps, personally. One way
around this would be to assume the default format is C[handle]_FORMAT,
meaning C$FILE's default format would be C$FILE_FORMAT. This would
make behavior very similar to current, and would make the above extra
step unnecessary. More clever ways of doing this probably exist as well.
Finally, note that if LRFC 174 is adopted, this can be made to look
even more simple and consistent:
open $FILE, "$file";
format $FILE, $FILE_FORMAT;# $FILE-format($FILE_FORMAT)
write $FILE; # $FILE-write
Since the indirect object and function syntaxes could be used
interchangeably.
=head1 IMPLEMENTATION
Hold on.
=head1 MIGRATION
There is a need for migration, but I'd rather save this until later
since this idea may get massively revised.
=head1 NOTES
[1] I personally disagree, but this RFC is close enough to make me
happy. :-)
[2] We might consider making a special case in the Perl parser so that
if a variable is declared of type Cformat then the Perl 5 syntax can
be used:
my format $FILE_FORMAT =
@: @
$name, $ssn
.
Then this is even less different and scary. Get rid of that Cmy and
it's Perl 5.
=head1 REFERENCES
RFC 174 (v1): Parse Cfunc($obj, @args) as Cfunc $obj (@args)
