Module::Pluggable? (search.cpan.org is your friend.)

Hopefully it isn't bad form to simply post links to a separate website, but last year I wrote about some plugin-type work I did with OpenInteract2. They talk about a fairly straightforward method to allow people to create plugins by having a module under a particular package anywhere in @INC, and having each plugin be able to specify enough metadata for an external process to order them as necessary.

• A little bit of Algorithm::Dependency and decomposition
• Using a lot lately: Factory + implementation autodiscovery

package Toolkit::DB;
#############################################
# new - constructor
#
#
# returns blessed db object
#############################################
sub new
{
    my $self = shift;
    my %params = @_;
    if (!$params{dbtype})
    {
        $params{dbtype} = "Toolkit::FileDB";
    }
    $params{delegate} = "$params{dbtype}"->new(%params);
     
    return bless \%params,$self;
}

#############################################
# insert - add a record to the db
#
# takes hash of fieldname/fieldcontent
#
# returns success/fail
#############################################
sub insert
{
    my $self = shift;
    my %data = @_;

    my $result = $self->{delegate}->insert(%data);

    return $result; 
}
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(With similar methods for all the other function calls needed). Then at run time you can choose which implementation class to use, or take the default ('Toolkit::FileDB' in this instance).

Update: It's just occurred to me - that way you could also create stubs for the functionality that return 'this function is not available without X::Y::Z installed' instead of a fatal error.

Update: There's some possibly related discussion about using use and require in Use and Require - making an informed choice.

BEGIN {
    if ($ENV{DBI_SQL_NANO} || !eval { require "SQL/Statement.pm" }) {
        @DBI::SQL::Nano::Statement::ISA = qw(DBI::SQL::Nano::Statement
+_);
        @DBI::SQL::Nano::Table::ISA     = qw(DBI::SQL::Nano::Table_);
    }
    else {
        @DBI::SQL::Nano::Statement::ISA = qw( SQL::Statement );
        @DBI::SQL::Nano::Table::ISA     = qw( SQL::Eval::Table);
    }
}
[download]