package My::FieldMap;

our %INTERNAL_VALUES = (
    'foo|bar' => 'fb_val'
);
our %INTERNAL_NAMES = (
    'foo|bar' => 'fb_val'
);

sub _build_key {
    return lc( join '|', @_);
}

sub get_internal_name_value {
    shift if $_[0] eq __PACKAGE__;  # Can call as pkg method
    my $ext_name = shift;
    my $ext_value = shift;

    my $composite_key = _build_key( $ext_name, $ext_value );

    # probably want to put some error checking code here.
    #    What do you do if called in scalar context?
    #    What if one or both keys don't exist?

    return (
        $INTERNAL_NAMES{$composite_key},
        $INTERNAL_VALUES{$composite_key}
    );
}
[download]

Use it like this:

my ($in,$iv) = My::FieldMap->get_internal_name_value( $ext_name, $ext_
+value );

# or
my ($in,$iv) = My::FieldMap::get_internal_name_value( $ext_name, $ext_
+value );
[download]

Now, when you have to deal with millions of field/name pairs, and you move to Redis or memcached to store them, you just have to update the lookup function.

A good interface with horrible code behind it is 10000% better than the most elegant snippets sprinkled everywhere.