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Re: Deprecating downgrade of `use utf8`

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Karl Williamson
February 21, 2022 23:33
Re: Deprecating downgrade of `use utf8`
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On 2/21/22 10:48, Ovid via perl5-porters wrote:
> On Monday, 21 February 2022, 18:32:34 CET, Paul "LeoNerd" Evans <> wrote:
>> On a similar note: How do people feel about code which turns off the
> "my source encoding is UTF-8" pragma after having previously turned it
> on? I.e.
>>    use utf8;
>>    my $café = "Ĉu vi havas sandviĉojn?";
>>    no utf8;
>> If we disallow this kind of thing, we can remove further weird
>> cornercases from the parser, because a bunch of unlikely situations no
>> longer come up.
>> As with VERSION: Are there any actually-valid use-cases for doing this
>> kind of thing?
>   Conversely, do we know of areas where "no utf8" causes problems in the Perl language intead of the perl core?
> Also, what are the problems in the perl core? Are they causing grief?
> Best,
> Ovid
> -- 

I don't see a compelling reason to change or remove 'no utf8'

The bugs I know about came from my reading code; not from any reported 
issues, and they involve switching encodings in mid-file

I think all we need say is that the behavior is undefined if your file 
contains multiple encodings in it.

Since ASCII is a proper subset of UTF-8, it should be fine to have 
sections of the file only in ASCII, and other sections allow complete 
UTF-8.  The proposed use source::encoding 'ascii' pragma can be used to 
demarcate such sections, if desired.

The only other possibility of multiple encodings in modern perl is 
Latin1 vs UTF-8.  Non-ASCII Latin1 characters have a different 
representation in UTF-8 than when not.  And I don't think it makes much 
sense for a Perl source to have both encodings.  The bugs arise when 
that happens.  If we say results are undefined for this behavior, we 
don't have to worry about it.

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