Yes, ok, I agree with you that my idea isn't suitable for the
preprocessor. If in the compiler instead, what issues do you see?

The use case I encounter most often when I wish I had reflection is
converting enums into strings...

enum Color { red, green, blue };
const char* color_name[] = {"red","green","blue"};
switch(n)
case red:
 printf("Activated %s\n", color_name[red];

I'd like a smaller solution than CppMeta C++ templates, to be able to
generate color_name strings in C code without explicitly writing the
color_name line of code. My issue with writing that line is if enum
Color changes I may forget to update color_name strings to match.

Ideas?

Robin Rowe
Beverly Hills, California
*Chairman ISO WG21 SG14 C++ Banking and Financial Systems Subcommittee

On 2/22/2024 4:13 PM, Jens Maurer wrote:
>
> On 21/02/2024 01.19, Robin Rowe via SG7 wrote:
>> Thank you for posting the insightful thread about CppMeta as a potential
>> implementation of C++ reflection. I'd like to ask about bringing code
>> reflection to C.
>>
>> I program in both C++ and C. I am imagining, for code reflection in C, a
>> new preprocessor operator ### (maybe called code-string) to go with #
>> (stringize) and ## (concatenate).
>
> Please read [lex.phases] (in C++) or 5.1.1.2 (in C23).
> The preprocessor runs way earlier than when C tokens are recognized as such.
>
> This won't work absent major surgery to foundational concepts of C
> (and C++, if a compatible facility should be introduced there).
>
> Jens
>
>
>> However, unlike # and ##, using ###
>> isn't limited to within a #define macro...
>>
>> // C preprocessor ### operator potential example:
>>
>> enum Color { red, green, blue };
>>
>> struct Point
>> { int x;//some comment
>> int y;
>> int z;
>> };
>>
>> void foo(int x);
>>
>> const char* s = ###(Color);
>> puts(s);
>> /* output:
>> enum Color { red, green, blue };
>> */
>> s = ###(Color.2);
>> puts(s);
>> /* output:
>> enum blue = 2;
>> */
>> s = ###(Point);
>> puts(s);
>> /* output:
>> struct Point
>> { int x;//some comment
>> int y;
>> int z;
>> };
>> */
>> s = ###(Point.x);
>> puts(s);
>> /* output:
>> int x;
>> */
>> s = ###(Point.1);
>> puts(s);
>> /* output (member #1):
>> int y;
>> */
>> s = ###(Point.);
>> puts(s);
>> /* output (how many members in struct):
>> 3
>> */
>> s = ###(foo);
>> puts(s);
>> /* output:
>> void foo(int x);
>> */
>> s = ###(Hello); //compile-time error, Hello doesn't exist
>>
>> Code-string hasn't been proposed yet. Still at idea stage. CppMeta is
>> much more sophisticated, seems too sophisticated for C. What are the
>> most significant features of CppMeta missing in ### concept?
>>
>> Thoughts?
>>
>> Robin Rowe
>> Beverly Hills, California
>> *Chairman ISO WG21 SG14 C++ Banking and Financial Systems Subcommittee
>>