- For the #define and ## I am thinking of striking the discussion other
   than to point out there is implementation divergence. Something like:

   There is implementation divergence on how the concat operator, ##, works
   with combining characters. The code below is flagged as an error today by
   gcc, it is accepted by clang and msvc.

    <#cb3-1>#define accent(x) x##\u0300 <#cb3-2> <#cb3-3>constexpr int
accent(A) = 2; <#cb3-4>constexpr int gv2 = A\u0300;
<#cb3-5>static_assert(gv2 == 2, "whatever");

   Compiler Explorer Link
   <https://godbolt.org/#g:!((g:!((g:!((h:codeEditor,i:(fontScale:14,j:1,lang:c%2B%2B,selection:(endColumn:37,endLineNumber:5,positionColumn:1,positionLineNumber:1,selectionStartColumn:37,selectionStartLineNumber:5,startColumn:1,startLineNumber:1),source:'%23define+accent(x)+x%23%23%5Cu0300%0A%0Aconstexpr+int+accent(A)+%3D+2%3B%0Aconstexpr+int+gv2+%3D+A%5Cu0300%3B%0Astatic_assert(gv2+%3D%3D+2,+%22whatever%22)%3B%0A'),l:'5',n:'0',o:'C%2B%2B+source+%231',t:'0')),k:50,l:'4',m:100,n:'0',o:'',s:0,t:'0'),(g:!((h:conformance,i:(compilers:!((compilerId:clang_trunk,options:''),(compilerId:gsnapshot,options:''),(compilerId:vcpp_v19_24_x64,options:'')),editorid:1,langId:c%2B%2B,libs:!()),l:'5',n:'0',o:'Conformance+viewer+(Editor+%231)+3/10',t:'0')),header:(),k:50,l:'4',n:'0',o:'',s:0,t:'0')),l:'2',n:'0',o:'',t:'0')),version:4>

   The ability to form valid identifiers via token pasting with combining
   characters is not a goal of this paper.






On Tue, May 26, 2020 at 5:26 PM Jens Maurer <Jens.Maurer_at_[hidden]> wrote:

> On 26/05/2020 22.51, Steve Downey via SG16 wrote:
> > Find attached a draft of the UAX31 paper for discussion.
> > Viewable at
> http://htmlpreview.github.io/?https://github.com/steve-downey/papers/blob/master/generated/p1949.html
> > Source at https://github.com/steve-downey/papers/blob/master/p1949.md
> >
> > (note that github doesn't format the same way that mpark's WG21 format
> does)
>
> Section 1, third bullet: add "be" (otherwise the sentence is missing a
> verb)
>
>
> "Note that #define and ## require identifiers as operands, and combining
> characters are generally not allowed as leading characters in identifiers.
>
> This is correct for #define, but not for ##.
> A pp-token is enough for ##; in particular, you can combine
> an identifier with a pp-number (which is not an identifier).
>
>
> "[ Note: In translation phase 4, identifier also includes those
> preprocessing-tokens (5.4 [lex.pptoken]) differentiated as keywords (5.11
> [lex.key]) in the later translation phase 7 (5.6 [lex.token]). – end note ]"
>
> Please make "identifier" and "preprocessing-token" italics (grammar
> references).
>
>
> Jens
>