Moose and Moo support Perl 5.8, but not 5.6. And we frequently see questions from people stuck with 5.8 on RHEL (and apparently unable/unwilling/forbidden from installing a newer local Perl). But it's quite unusual to find a CPAN tester still smoking distributions on Perl's that precede 5.6. Perl's newest features are fantastic for in-house code, but I believe CPAN code ought to be more portable.

I look at it this way; When I put something up on CPAN it's so that others might get some use out of something that I found to be useful. If I'm going to go to the effort of creating a distribution, I may as well do so for as broad a base as I can. Supporting older Perl versions is sort of like supporting a broad range of OS's. I cannot guess who will be using a module, what OS they'll be using, or what Perl version they will have. If I choose not to support a version or an OS, I am placing a limit on who might be able to use the module. Perhaps that's ok. To the extent that it's practical, I prefer to minimize the requirements placed on the user's Perl environment -- at least the requirements that I'm not able to affect.

One thing I try to do is look at what dependencies I really need, and what requirements they impose as well. If I can't live without Moo, then I'm going to have to give up Perl 5.6, so I may as well code to 5.8+. If I can't reasonably live without a module that requires 5.10, then I may as well code to 5.10+ as well. But what I try not to do is code to 5.10 when all of my dependencies are capable of running under 5.6.

Having said all that, I don't give a second thought to pre-5.6.

One module that I'm involved in currently has dependencies that require 5.8, but I'm in the process of re-working it to use a different dependency so that I can support 5.6 too. (The change in dependencies gets me a few other improvements too, in this case). And this all started with a kind message from someone who has provided useful feedback on some of my other work. In this case the request went something like this: "It would be useful to me if XYZ could support 5.6, and here's what I can do to help in that regard." So there are still those out there who have a need, and some of them are appreciative and willing to extend a helpful hand in recapturing some backward compatibility.

This feature is available starting with Perl 5.10.

I don't think it's unreasonable to expect people to be using at least Perl 5.10.

OK, so there are a bunch of legacy Perl 5.8 and even 5.6 installations out there, but these people shouldn't be expecting to be able to download brand new releases from CPAN.

My own policy is to generally target 5.10, but if I can support 5.8 or earlier without too much extra trouble, then do so (especially on Tiny-style modules). A handful of my distributions even require Perl 5.12 or 5.14.

package Cow { use Moo; has name => (is => 'lazy', default => sub { 'Mooington' }) } say Cow->new->name

There is no standard Perl version for Perl 5, unlike Perl 6 which started with a standard. As for me, I'm comfortable with any Perl version thrown at me:-).

The answer is in regen/feature.pl:

# just the relevant bits and pieces
my %feature = (
    say             => 'say',
    state           => 'state',
    switch          => 'switch',
    evalbytes       => 'evalbytes',
    array_base      => 'arybase',
    current_sub     => '__SUB__',
    lexical_subs    => 'lexsubs',
    unicode_eval    => 'unieval',
    unicode_strings => 'unicode',
    fc              => 'fc',
    );

my %feature_bundle = (
     all     => [ keys %feature ],
     default => [qw(array_base)],
    "5.9.5"  => [qw(say state switch array_base)],
    "5.10"   => [qw(say state switch array_base)],
    "5.11"   => [qw(say state switch unicode_strings array_base)],
    "5.13"   => [qw(say state switch unicode_strings array_base)],
    "5.15"   => [qw(say state switch unicode_strings unicode_eval eval
+bytes current_sub fc)],
    "5.17"   => [qw(say state switch unicode_strings unicode_eval eval
+bytes current_sub fc)],
    );
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I have suggested to the developers to add this information to Module::CoreList as a new option -f.

   -------------------------------------
 | file  | explicit | syntax  | external |
 | ------------------------------------- |
 | yo.pl | ~        | v5.10.0 | n/a      |
 | ------------------------------------- |
 | Minimum explicit version : ~                             |
 | Minimum syntax version   : v5.10.0                       |
 | Minimum version of perl  : v5.10.0                       |
   -------------------------------------
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