On Mon, May 9, 2022 at 5:14 PM Tom Honermann via SG16 <sg16@lists.isocpp.org> wrote:
On 5/8/22 4:04 PM, Barry Revzin via SG16 wrote:


On Sun, May 8, 2022 at 9:22 AM Victor Zverovich <victor.zverovich@gmail.com> wrote:
> One thing I noticed is that the wording about Grapheme_Extend is gone. I didn't know what this meant before, so I don't know now if this is a good removal or a bad removal.

I don't recall any requests for removing it and think that it should be reintroduced.

- Victor

On Wed, May 4, 2022 at 10:44 PM Jens Maurer <Jens.Maurer@gmx.net> wrote:
On 05/05/2022 04.08, Barry Revzin wrote:
> I think I have applied this. Here's the rendered version: https://brevzin.github.io/cpp_proposals/2286_fmt_ranges/p2286r8.html#pnum_12 <https://brevzin.github.io/cpp_proposals/2286_fmt_ranges/p2286r8.html#pnum_12>

> How does this look?

p2.2

For each code sequence X in S that either encodes a single character or encoding state transition or that is a sequence of ill-formed code units is processed in order as follows:

That feels like bad English grammar to me.

Why "encoding", yet there is an "encodes" before that?
Why "either" and there are three things that don't
exactly correspond grammatically?

Maybe make a bulleted sub-list with the three items
so that the structure is clear.

"If C is one of the UCS scalar values the table below,"

add "in"

better clarify: "the two characters shown as the
corresponding escape sequence are appended to E"


after p2.3.4, p2.5

"simple-hexadecimal-digit-sequence"

I would not re-use lexing grammar for a local placeholder,
just say \u{/hex-digit-sequence/} or so.


p2.5

"Otherwise, X is a sequence of ill-formed code units. Each"

-> "Otherwise (X is a sequence of ill-formed code units), each code unit ..."


"U+0027 APOSTROPHE is escaped as \' while U+0022 QUOTATION MARK is left unchanged."

Can we rephrase that to avoid "is escaped as"?  We were on such a good
track to just append characters and avoid any judgment calls.

suggestion "
 - for each character U+0027 APOSTROPHE in S, the two characters \' are appended to E
 - U+0022 QUOTATION MARK is left unchanged"


Jens

Thanks Jens and Victor! I did my best to apply the suggested changes:


Hopefully, this gradient is slowly descending to the correct solution :-)

Thanks, Barry. This appears to have incorporated the parts of my prior suggestions that did not have opposition, so just minor issues noted below.

Discussion at the last meeting revealed that we're failing to specify the encoding used to interpret S. Change p2 as follows: (perhaps substitute "as described below" for "as follows")

The escaped string E representation of a string S is constructed by encoding a sequence of characters as follows. in tThe associated character encoding CE for charT ([lex.string.literal]) as follows: is used both to interpret S and to construct E.

In p2.2, "code sequence" -> "code unit sequence".

In p2.3.4 and p2.5, I don't think we should re-use the hexadecimal-digit grammar term here. Just say, "hexadecimal digits".

Add the following note to p2.4 to address a request by Hubert:

Otherwise, if X encodes a state transition, the effect on E is unspecified. [ Note: the intent is that a state transition be represented in E such that its original code unit sequence can be reconstructed - end note ]

I think this needs to be:

Otherwise, if X encodes a state transition, the effect on E<ins> and further decoding of S</ins> is unspecified. [ Note: the intent is that a state transition be represented in E such that<del> its</del><ins> the</ins> original code unit sequence<ins> of S</ins> can be reconstructed -end note ]
 
The issue being that I am not aware of widespread implementation experience indicating that observing the state transition in the decoding is a "win".
Indeed, problems can already be anticipated.

For example, how would a lack of return to the initial encoding state prior to \0 be represented?

Regardless of what the Core language wording recommends about managing state transitions in encoding of string literals, there may be external requirements that cause an implementation to encode returns to the initial shift state prior to numeric escapes. Once E is placed into a non-initial shift state, there may simply be no way to follow these rules without introducing additional shift states not originally present.


Hubert pointed out during the last meeting that we should not be trying to interpret state transitions for stateful encodings as I had previously been trying to do. I think we can now simplify p2.5:

Otherwise (X is a sequence of ill-formed code units), each code unit U is appended to E in order as the sequence \x{hex-digit-sequence}, where hex-digit-sequence is the shortest hexadecimal representation of U using lower-case hexadecimal digits. When encoding a stateful character encoding, these additions should have no effect on encoding state.

In p3, we now need to drop "in a Unicode encoding". I think the result should also produce a string, not a character.

The escaped characterstring representation of a character C in a Unicode encoding is equivalent to the escaped string representation of a string of C, except that:

p4 should be removed now.

The escaped character and escaped string representations of a character or string in a non-Unicode encoding is unspecified.

Hubert, the wording does not explicitly address your request to be able to specify spacing and separator characters as a set of encoding agnostic code point values. I think the existing wording suffices to meet your goals since an implementation can document a method of identifying the set of escaped characters by, for example, specifying characters in EBCDIC 1047 and describing how to map those to other code pages. If you don't agree, could you suggest how the wording might be updated to better address your concern?

I think that interpretation works.
 

Tom.


Barry

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