In my new position we have a large set of code to manage. Most of it is Perl 5.12, using a set of modules which must be getting out of date.

That's not necessarily a big concern now, they do their job. But when we need new features, at some point, we want to be able to install new versions of modules while keeping the old versions around. Existing code can run old versions, until they need to be updated for some other reason, then they can be updated and tested.

The alternative is to modify and test an overwhelming amount of code at the same time, or else to risk upgrading all the programs at once, without individual testing. Don't like either of those alternatives.

I see Ingy wote a module 'only' back in 2005 ...

use only Class::Date => '1.1.8-1.1.10';
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Is that the best system to use? or are there alternatives?