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=head1 TITLE
Replace Exporter by a better scaling mechanism
=head1 VERSION
Maintainer: Ilya Zakharevich <[EMAIL PROTECTED]>
Date: 15 September 2000
Mailing List: [EMAIL PROTECTED]
Number: 233
Version: 1
Status: Developing
=head1 ABSTRACT
This RFC proposes a minimal efficient well-scaling mechanism for exporting.
Only export of subroutines and tags are supported by this mechanism.
=head1 DESCRIPTION
C<Exporter> gives an enormous efficiency hit for modules with a large
list of exportable symbols (but which are very small nevertheless, say,
because everything is autoloaded). It is supposed to be optimized for
speed, with a lot of caching and keeping things close at hand. However,
all these actions are in fact only slowing things down, since they create
a lot of code to compile, and a lot of data structures to maintain.
In many cases the Exporter-support data creates up to 90% of memory overhead
of the module (so may be supposed to provide a similar fraction of the load
time overhead).
Lessons learned:
=over
=item *
instead of keeping a lot of arrays and a hash storing a lot of redundant data,
store the information in a string, and use RExen to extract it from
this string.
This provides a crucial advantage in the memory footprint, and may provide
speed advantages (maybe even if the module is imported from many times).
This string may contain items of two kinds: symbols, and tag lists of the
form C<":tag[ :subtag1 :subtag2 symbol1 symbol2 ]">. If symbols appears
inside a tag, it need not be repeated again. The default exporting list
should be provided the same as the list for the C<:DEFAULT> tag.
=item *
The symbols may be followed by the prototypes. Example:
' :DEFAULT[:micro :mini additional_f(\%)] :micro[ func1($$) ]
:mini[ func2($) ] :extra[ func3() ] func4($) '
Having the prototypes in this list may be useful, since the same list
may be used by the compile-time action of autoloading, reducing the
overhead yet more. (See RFC on flexible autoloading.)
=item *
The export string should be registered as the argument to the pragma.
Example:
use export q( func1($$) func2($) ); # No default
=item *
The export list may be substituted by a subroutine reference which returns
such a string (cached to avoid such a call for future exporting). Example:
use export sub { local $/; my $l = <DATA>; eval 'use export $l'; $l };
...
__DATA__
func1($$)
func2($)
This is desirable since the subroutine may be autoloaded (either explicitly,
or as above), thus reducing yet more the overhead of import-less
use Module ();
=item *
export.pm should support only this barebone API. Anything hairer
should be implicitly requested via a separate module (Export::Methods),
so that the overhead of export.pm is as small as possible.
=back
=head1 MIGRATION ISSUES
None.
=head1 IMPLEMENTATION
Straightforward.
=head1 REFERENCES
None.
