How do you do multi-version modules?

[perl-diddler]

I have a module I created .. and realized I wanted to change something in the interface. So... I've been 'versioning' each module change, and would bump the version in the new module.. BUT, how could my module detect -- when a user says: "use module 1.0.0", and I'm working in module "2.0.0"? My 2.0.0 module would never get called as far as I can tell...no?

What I would want to do is have my 2.0.0 module detect if it was called by something prior to 2.0, and apply the old interface semantics for compatibility.

The only way I can think of is to NOT version my code, but expect that any "using modules" will use "some version" (which? .. How would they know if I don't put a version in my code?) but then if I was called as a versionless module, I think I might receive the version number as a parameter, and could then implement the behavior I want -- but it seems that to do that I have to NOT use a version number -- which would sorta make it hard for any new code to know what version to specify to get behavior "X"...

Is it possible to do this? Or prohibitively difficult?

Thanks for ideas, suggestions, clue-sticks!...

Linda