stable - Experimental features made easy, once we know they're stable


version 0.032


use stable 'lexical_subs', 'bitwise';
my sub is_odd($value) { $value & 1 }


The experimental pragma makes it easy to turn on experiments while turning off associated warnings. You should read about it, if you don't already know what it does.

Seeing use experimental in code might be scary. In fact, it probably should be! Code that uses experimental features might break in the future if the perl development team decides that the experiment needs to be altered. When experiments become stable, because the developers decide they're a success, the warnings associated with them go away. When that happens, they can generally be turned on with use feature.

This is great, if you are using a version of perl where the feature you want is already stable. If you're using an older perl, though, it might be the case that you want to use an experimental feature that still warns, even though there's no risk in using it, because subsequent versions of perl have that feature unchanged and now stable.

Here's an example: The postderef feature was added in perl 5.20.0. In perl 5.24.0, it was marked stable. Using it would no longer trigger a warning. The behavior of the feature didn't change between 5.20.0 and 5.24.0. That means that it's perfectly safe to use the feature on 5.20 or 5.22, even though there's a warning.

In that case, you could very justifiably add use experimental 'postderef' but the casual reader may still be worried at seeing that. The stable pragma exists to turn on experimental features only when it's known that their behavior in the running perl is their stable behavior.

If you try to use an experimental feature that isn't stable or available on the running version of perl, an exception will be thrown. You should also take care that you've required the version of stable that you need!

If it's not immediately obvious why, here's a bit of explanation:

Sure, it's a little weird, but it's worth it! The documentation of this pragma will tell you what version of stable you need to require in order to use various features. See below.

At present there are only a few "stable" features:


perlexperiment contains more information about experimental features.


Leon Timmermans <>


This software is copyright (c) 2013 by Leon Timmermans.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.