RFC: Hole In The Middle Pattern (Was Data Driven Programming)

[bennymack]

Dear Monks,

I'd like to do a quick follow up on Data driven programming? Not sure. I've come up with a much simpler, much more naive implementation that requires much less code to implement but still gives approximately the same affect. This new implementation does zero string evals, and no longer uses attributes.

The new implementation is called "ReRequire" and simply deletes a given module name from %INC and re-requires it (hence the name). This essentially means that modules that are written to be re-requirable are code compartments that allow the re-definition of constants at compile and run time.

Here is a quick example of Package::ReRequire in use.

Package::ToBeReRequired

package Package::ToBeReRequired1;
use strict;
use Carp();

use Package::ReRequire(
    CLUCK     => 0,
    METHOD    => 0,
    CONDITION => 0,
    THING     => 'default_thing',
);

sub get_sub {
    use warnings;
    return sub {
        my( $self ) = @_ if METHOD;
        my( $output ) = ( METHOD ) ? $self : '';
        if( CONDITION ) {
            $output .= ' CONDITION ';
        };
        $output .= ' UNCONDITIONAL ';
        $output .= THING;
        Carp::cluck __CALLER__ . ' clucking ' if CLUCK;
        return $output;
    };
}

1;

__END__

Package::ReRequire1

package Package::ReRequire1;
use strict;
use warnings;
# use Data::Dumper; $Data::Dumper::Terse=1;

use Package::ReRequire();

sub import {
    Package::ReRequire::rerequire(
        'Package::ToBeReRequired1',
        CLUCK     => 0,
        METHOD    => 0,
        CONDITION => 1,
        THING     => __PACKAGE__,
    );
    
    *function = Package::ToBeReRequired1::get_sub();
}

1;

__END__

Package::ReRequire2

package Package::ReRequire2;
use strict;
use warnings;
# use Data::Dumper; $Data::Dumper::Terse=1;

use Package qw[ReRequire];

sub import {
    ReRequire::rerequire(
        'Package::ToBeReRequired1',
        CLUCK     => 1,
        METHOD    => 1,
        CONDITION => 0,
        THING     => __PACKAGE__,
    );

    *method   = Package::ToBeReRequired1::get_sub();
}

1;

__END__

Then, you can do something like this to see what this is turned into:

$ perl -Mwarnings -e ' use B::Deparse; use Package::ReRequire1;  print
+f( "%s = %s\n", $_, B::Deparse->new->coderef2text( \&{ "Package::ReRe
+quire1::" . $_ } ) ) for keys %{ "Package::ReRequire1::" };'
function = {
    package Package::ToBeReRequired1;
    BEGIN {${^WARNING_BITS} = "UUUUUUUUUUUU"}
    use strict 'refs';
    '???';
    my($output) = '';
    do {
        $output .= ' CONDITION '
    };
    $output .= ' UNCONDITIONAL ';
    $output .= 'Package::ReRequire1';
    '???';
    return $output;
}
BEGIN = ;
import = {
    package Package::ReRequire1;
    BEGIN {${^WARNING_BITS} = "UUUUUUUUUUUU"}
    use strict 'refs';
    Package::ReRequire::rerequire('Package::ToBeReRequired1', 'CLUCK',
+ 0, 'METHOD', 0, 'CONDITION', 1, 'THING', 'Package::ReRequire1');
    *function = Package::ToBeReRequired1::get_sub();
}


$ perl -Mwarnings -e ' use B::Deparse; use Package::ReRequire2;  print
+f( "%s = %s\n", $_, B::Deparse->new->coderef2text( \&{ "Package::ReRe
+quire2::" . $_ } ) ) for keys %{ "Package::ReRequire2::" };'
BEGIN = ;
method = {
    package Package::ToBeReRequired1;
    BEGIN {${^WARNING_BITS} = "UUUUUUUUUUUU"}
    use strict 'refs';
    my($self) = @_;
    my($output) = $self;
    '???';
    $output .= ' UNCONDITIONAL ';
    $output .= 'Package::ReRequire2';
    Carp::cluck('Package::ReRequire2 clucking ');
    return $output;
}
import = {
    package Package::ReRequire2;
    BEGIN {${^WARNING_BITS} = "UUUUUUUUUUUU"}
    use strict 'refs';
    ReRequire::rerequire('Package::ToBeReRequired1', 'CLUCK', 1, 'METH
+OD', 1, 'CONDITION', 0, 'THING', 'Package::ReRequire2');
    *method = Package::ToBeReRequired1::get_sub();
}

To download the code and see the full test suite, check out:

$ export CVSROOT=:pserver:[e-mail]:/home/ben/documents/cvsro
+ot
$ cvs co my_modules

Creative name, I know! Ok, that's all for now. Let me know what you think. The interface is certainly not finalized. It's just the first thing I settled on that looks usable. All suggestions will be considered. Patches welcome. Thanks!

Update: Added more examples.