The CPAN module Class::Factory encapsulates all this for you -- just tell your factory about the different implementations and type associated with each, then pass that type to the factory when you want a new object.

You can do

$mod = 'My::Module1';
eval "use $mod";
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which is the same as

$mod = 'My::Module1';
($mod_file = $mod) =~ s{::}{/}g;
$mod_file .= '.pm';
require $mod_file;
$mod->import if $mod->can('import');
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The first two snippet imports the symbols if the module uses Exporter or similar. However, instead of importing, it be safer to do

$mod = 'My::Module1';
eval "require $mod";

$mod->function();
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The last snippet requires that function accept an extra initial argument.

eval "require $your_class_name";
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Just require the modules and don't import the functions that have the same name; invoke them using their fully qualified names. E.g. if both Module1 and Module2 have foo:

require Module1;
require Module2;

Module1::foo();
Module2::foo();
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my $mod = some_condition() ? 'Module1' : 'Module2';
eval "require $mod; ${mod}::foo()";
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TIMTOWTDI: I find the problem description admits too many different interpretations, leading to entirely different solutions; anyway, here's another possible form the solution could take:

use strict;
use warnings;

my $mod = shift;

require "$mod.pm";

eval "$mod->import(); 1" or die;  # modules all export 'foo' by defaul
+t
# eval "$mod->import( 'foo' ); 1" or die;

foo();
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eval "require $modName";
if( $@ ){
 die("Cannot load $modName : $@");
}
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