It's been a while since I've played with carton, but having to use carton exec to start the software is less than ideal imo, and I'm still not sure that it allows for the same application to be running multiple versions of a package. Picking a particular version of a library is pretty straight forward, it's running multiple at the same time that stumps me. Here's some code I put together to pick a particular version:

package LoadModule;
use strict;
use warnings;


my $wantedPackages;
my $INC_LOADED;

sub import
{
    my $pkg = shift;
    my ($module, $version) = @_;

    $wantedPackages->{$module} = $version;
    push(@INC, \&loadLib) unless($INC_LOADED);
    $INC_LOADED = 1;
}

sub loadLib
{
    my ($codeRef, $filename) = @_;

    my $moduleName = $filename;
    # Strip the implied pm
    $moduleName =~ s/\.pm$//;

    if(exists $wantedPackages->{$moduleName})
    {
        my $package = $moduleName . "-" . $wantedPackages->{$moduleNam
+e} . ".pm";
        if(-e "./lib/$package")
        {
            my $fh;
            open($fh, "<", "./lib/$package") || die "Can't open ./lib/
+$package: $!";
            return($fh);
        }
    }
    else
    {
        return undef;
    }
}
1;
[download]

package TestModule1;

use LoadModule MyLib => 'v1';
use MyLib;

sub doPrint
{
    MyLib::foo();
}
1;
[download]

In the example above I have

lib/MyLib-v1.pm
and
lib/MyLib-v2.pm
[download]

Tihs works great for the first module loaded. However, if I load other version of the same module they don't seem to get loaded (I suspect there's namespace collision).

However, if I load other version of the same module they don't seem to get loaded (I suspect there's namespace collision).

Yeah, namespaces are global

If you're improving the API, why not improve the names?

If you module was OOpy it could be much simpler, simply export a sub that returns the name of the subclass ... or just make sure the caller inherits from it

You could simply disallow fully qualified names (MyLib::Foo()) and simply export the appropriate sub Foo

And there is always source filters