I agree that simply using perl 5.12 gets you most of Perl 5.12. Specifically, you get bug fixes and features that aren't backwards incompatible. For the rest of the features, you need the pragma.

Did you mean you found a convoluted way (which I did not understand) to describe use 5.012;?

Saying that use 5.012; causes the Perl 5.12 language to be used is hardly convoluted. But no, I wasn't describing use 5.012;, I was talking about strict in Perl 5.12.

*Most* changes of the language you'll get with, or without use 5.XXX. (Smart match for instance, all of the regexp changes, new versions of Unicode, etc).

Actually, some of the regex and unicode changes require use 5.xxx; because they aren't backwards compatible.

Second, due to exporting, one actually needs to run code to know what's being exported

Granted, I forgot that.

Let's say it was impossible to export variables. Would you still say that use strict 'vars'; should be done by a linter instead of Perl itself?

The point is I think your condition for deciding if something should be done by a linter instead of perl is insufficient. This renders your argument unconvincing.

But no, I wasn't describing use 5.012;, I was talking about strict in Perl 5.12.

Now I'm utterly confused, and I've no longer the faintest clue what you're trying to say. If I run the binary that I build with the source that comes in the perl 5.12 tarball, I only get strictness by either 1) doing use strict;, and 2) use 5.012;. 1) certainly isn't new to 5.12, and you seem to disagree with me on 2). Can you show some code that shows strict on by default, with the use 5.012; clause?

Actually, some of the regex and unicode changes require use 5.xxx; because they aren't backwards compatible.

Could you elaborate on this one? Which regexp or Unicode feature is only available after doing a use 5.012;? According to man feature, the only features are:

   The ’switch’ feature
       "use feature 'switch'" tells the compiler to enable the Perl 6
       given/when construct.

       See "Switch statements" in perlsyn for details.

   The ’say’ feature
       "use feature 'say'" tells the compiler to enable the Perl 6 "say"
       function.

       See "say" in perlfunc for details.

   the ’state’ feature
       "use feature 'state'" tells the compiler to enable "state" variables.

       See "Persistent Private Variables" in perlsub for details.

   the ’unicode_strings’ feature
       "use feature 'unicode_strings'" tells the compiler to treat all strings
       outside of "use locale" and "use bytes" as Unicode. It is available
       starting with Perl 5.11.3.

       See "The "Unicode Bug"" in perlunicode for details.

Now, checking perlunicode, it's suggested that if the unicode_strings feature is in effect, Unicode semantics will be in effect on all strings (as long as use locale and use bytes aren't in effect), in particular when it comes to /\w/ and lc/uc. But that doesn't actually seem to work:

$ perl -wE 'my $foo = "ë"; say $foo =~ /\w/ || 0; say uc $foo'
0
ë
$ perl -wE 'my $foo = "ë"; utf8::upgrade $foo; say $foo =~ /\w/ || 0; 
+say uc $foo'
1
ë
$
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Note though that I wasn't thinking of this feature when I was talking about Unicode changes - I was thinking about Perl 5.12 implementing Unicode 5.2 (as opposed to Unicode 5.0.0 in 5.10).

Let's say it was impossible to export variables. Would you still say that use strict 'vars'; should be done by a linter instead of Perl itself?

Probably not. The problem is that "use strict 'vars';" creates compilation errors. Linters typically don't check for that - they warn about valid, but (for some value of) questionable constructs. qw[hello, world] is certainly valid, and some think it to be questionable.

Now I'm utterly confused, and I've no longer the faintest clue what you're trying to say.

Ask a twisted question, get a twisted answer.

you seem to disagree with me on 2).

Nope.

But that doesn't actually seem to work:

Not for regex, unfortunately, but it does for uc

$ perl -CS -wE'no  feature qw( unicode_strings ); $_="\xEB"; utf8::dow
+ngrade($_); say /\w/||0; say uc;'
0
ë

$ perl -CS -wE'no  feature qw( unicode_strings ); $_="\xEB"; utf8::upg
+rade($_);   say /\w/||0; say uc;'
1
Ë

$ perl -CS -wE'use feature qw( unicode_strings ); $_="\xEB"; utf8::dow
+ngrade($_); say /\w/||0; say uc;'
0
Ë

$ perl -CS -wE'use feature qw( unicode_strings ); $_="\xEB"; utf8::upg
+rade($_);   say /\w/||0; say uc;'
1
Ë
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I think you had UTF-8 source code without using use utf8;.

I was thinking about Perl 5.12 implementing Unicode 5.2 (as opposed to Unicode 5.0.0 in 5.10).

Yes, you get that for free.

$ corelist -a Unicode

Unicode was first released with perl v5.6.2
  v5.6.2     3.0.1     
  v5.8.0     3.2.0     
  v5.8.1     4.0.0     
  v5.8.2     4.0.0     
  v5.8.3     4.0.0     
  v5.8.4     4.0.1     
  v5.8.5     4.0.1     
  v5.8.6     4.0.1     
  v5.8.7     4.1.0     
  v5.8.8     4.1.0     
  v5.8.9     5.1.0     
  v5.9.0     4.0.0     
  v5.9.1     4.0.0     
  v5.9.2     4.0.1     
  v5.9.3     4.1.0     
  v5.9.4     4.1.0     
  v5.9.5     5.0.0     
  v5.10.0    5.0.0     
  v5.10.1    5.1.0     
  v5.11.0    5.1.0     
  v5.11.1    5.1.0     
  v5.11.2    5.1.0     
  v5.11.3    5.2.0     
  v5.11.4    5.2.0     
  v5.11.5    5.2.0     
  v5.12.0    5.2.0     
  v5.12.1    5.2.0     
  v5.12.2    5.2.0     
  v5.13.0    5.2.0     
  v5.13.1    5.2.0     
  v5.13.2    5.2.0     
  v5.13.3    5.2.0     
  v5.13.4    5.2.0
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