> On Jun 16, 2023, at 3:21 AM, Martin Uecker <uec...@tugraz.at> wrote:
>
> Am Donnerstag, dem 15.06.2023 um 16:55 +0000 schrieb Joseph Myers:
>> On Thu, 15 Jun 2023, Qing Zhao via Gcc-patches wrote:
>>
> ...
>>> 1. Update the routine “c_parser_postfix_expression” (is this the right
>>> place? ) to accept the new designator syntax.
>>
>> Any design that might work with an expression is the sort of thing that
>> would likely involve many iterations on the specification (i.e. proposed
>> wording changes to the C standard) for the interpretation of the new kinds
>> of expressions, including how to resolve syntactic ambiguities and how
>> name lookup works, before it could be considered ready to implement, and
>> then a lot more work on the specification based on implementation
>> experience.
>>
>> Note that no expressions can start with the '.' token at present. As soon
>> as you invent a new kind of expression that can start with that token, you
>> have syntactic ambiguity.
>>
>> struct s1 { int c; char a[(struct s2 { int c; char b[.c]; }) {.c=.c}.c]; };
>>
>> Is ".c=.c" a use of the existing syntax for designated initializers, with
>> the first ".c" being a designator and the second being a use of the new
>> kind of expression, or is it an assignment expression, where both the LHS
>> and the RHS of the assignment use the new kind of expression? And do
>> those .c, when the use the new kind of expression, refer to the inner or
>> outer struct definition?
>
> I would treat this is one integrated feature. Essentially .c is
> somthing like this->c for the current struct for designated
> initializer *and* size expressions because it is semantically
> so close.
Yes, I think this is reasonable. (Is “this” the immediate containing structure?)
> In the initializer I would allow only
> the current use for designated initialization for all names of
> member of the currently initialized struct, so .c = .c would
> be invalid.
Given “.c” basically is “this->c”, then .c = .c should be considered as
this->c = this->c, is such self-initialization allowed in C?
> It should never refer to the outer struct if there
> is a member with the same name in the inner struct, i.e. the
> outside member is then hidden.
Does the above mean: if there is NO name conflicting, it could refer to a
field of an outer struct?
Why this is allowed? Why just disallow all referring to the field of the outer
structure since .c basically is this->c?
>
> So this would be ok:
>
> struct s1 { int d; char a[(struct s2 { int c; char b[.c]; }) {.c=.d}.c]; };
>
> Here the use of .d would be ok because it is not from the struct
> currently initialized, but from an outside scope.
I think that the above .c=.d should report an error, since .d does not exist in
the containing structure.
Do I miss anything here?
thanks.
Qing
>
> Martin
>
>
>
>
