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RFC 249 (v1) Use pack/unpack for marshalling

From:
Perl6 RFC Librarian
Date:
September 17, 2000 22:39
Subject:
RFC 249 (v1) Use pack/unpack for marshalling
Message ID:
20000918053904.18156.qmail@tmtowtdi.perl.org
This and other RFCs are available on the web at
  http://dev.perl.org/rfc/

=head1 TITLE

Use pack/unpack for marshalling

=head1 VERSION

  Maintainer: Ilya Zakharevich <ilya@math.ohio-state.edu>
  Date: 16 September 2000
  Mailing List: perl6-language-data@perl.org
  Number: 249
  Version: 1
  Status: Developing

=head1 ABSTRACT

This RFC extends pack/unpack builtins to store/extract the TEMPLATE to/from
the packed data.  This allows storage of arbitrary Perl data.

=head1 DESCRIPTION

=over

=item C<t>

on unpack(): remove the last extracted value and use it as if it replaces
this C<t>.  For example, the following two calls are equivalent:

  unpack 'A5  t A5', 'aCx6,AcX6...0123456'
  unpack 'aCx6, A5',      'AcX6...0123456'

on pack(): store the next argument so that it is extractable with C<'t'>,
this C<t> acts as a modifier for the previous type.  For example,

  pack 'A3 t', [5,6,[7,8],0]

may be stored in many ways, one of them (most readable?)

  'A7t' . ' A21 t ' . ' g[ A A g[ A A ] A ] ' . '56780'

When this is unpacked with C<'A3 t'>, the first 3 chars are used as a new
template, then the next 7 chars are used as a new template, then the next
21 chars are used as a new template, which finally extracts the structure.

This example shows that an arbitrary large structure can be extracted using
the template C<'A3 t'>.

=item C<T>

behaves the same as the C<A4 t>.  (Syntactic sugar, optional).  As shown
above, arbitrary data is restorable by a simple 'T'.  For example,

  pack 'T', [5,6,[7,8],0]

may be stored in many ways, one of them (most readable?)

  'A21t' . ' g[ A A g[ A A ] A ] ' . '56780'

=back

=head1 MIGRATION ISSUES

None.

=head1 IMPLEMENTATION

Straightforward.

=head1 REFERENCES

RFC142: Enhanced Pack/Unpack

RFC 246: pack/unpack uncontrovercial enhancements

RFC 248: enhanced groups in pack/unpack




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