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Subject: Re: Agenda for the 2021-04-28 SG16 telecon
From: Tom Honermann (tom_at_[hidden])
Date: 2021-04-27 12:51:57


On 4/27/21 1:43 PM, Corentin Jabot wrote:
>
>
> On Tue, Apr 27, 2021 at 7:20 PM Tom Honermann <tom_at_[hidden]
> <mailto:tom_at_[hidden]>> wrote:
>
> On 4/27/21 12:27 PM, Corentin Jabot wrote:
>>
>> I think we've been focusing on different things here. 
>> The issue I'm trying to discuss is independent of use of
>> the write-directly-to-the-console method.  This
>> discussion is about having std::print() (and
>> std::format()) internally ensure that that format
>> arguments provided by the locale are transcoded to match
>> the encoding of the format string.  This happens before
>> anything is written to the console; this is the step
>> where the formatting is done and the intent is to ensure
>> that well-formed text is produced *before* it is
>> transcoded to the native console encoding (whether that
>> be UTF-8, UTF-16, whatever).  Transcoding requires
>> well-formed input of course.
>>
>> Does this help to get us on the same page
>>
>>
>> I actually disagree with that.
>> I don't think there is intent in the current design that the
>> output has to be text at all. I could use format to create some
>> kind of binary format if i wanted to, except the _formatting_
>> string is text because it needs to be parsed,
>> So format as specified doesn't put requirements on  the arguments
>> beyond the formatting string and doesn't need to.
>> What makes print text is that it outputs to the console, at which
>> point text is assumed.
>> The transcoding  happens after formating, and might as well not
>>
>> forrmat(a, b, c) -> result
>> printUtf8ToConsole(result);
>>
>> The fact that printUtf8 is implemented as
>> printUTF16(toUTF16(result)) is an implementation detail that
>> should not be observable nor described by the C++ standard.
>>
>> And I don't think print should do _anything_ to check for some
>> amount of validity before  printing out something.
>>
> I don't disagree with what you wrote above, but it is not relevant
> to this discussion.  I don't know why we're having such a hard
> time communicating here.  Please, carefully re-read some of my
> prior responses with the understanding that how you have
> understood them so far does not match what I intended.  If you
> then have clarifying questions, please feel free to ask them.
>
>
> Okay, so your point is that implementations should do something
> magical for things that are formatted through a locale facet on the
> basis the encoding of the result of time_put is known?

Yes, with two minor caveats.

 1. I don't see this as magical since the source and target encodings
    are known.
 2. I'm only suggesting this as a design option for us to consider.  I'm
    not claiming that I think this is the best approach to the problem
    (I'm undecided as to what solution I favor so far).

Tom.



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