Use templates to avoid repetition, and to add type safety

[alejandro-colomar]

Cc: @uecker
Cc: @chrisbazley

This is an experiment about mimicking templates in C with macros. If we get rid of the trailing \, this looks quite nice.

[uecker]

Am Montag, dem 10.03.2025 um 09:39 -0700 schrieb Alejandro Colomar:

@alejandro-colomar commented on this pull request. In lib/atoi/strtoi/strton.h: > + \ + if (*endp == s) \ + *status = ECANCELED; \ + else if (errno == ERANGE || n < min || n > max) \ + *status = ERANGE; \ + else if (**endp != '\0') \ + *status = ENOTSUP; \ + else \ + *status = 0; \ + \ + errno = e; \ + \ + return MAX(min, MIN(max, n)); \ +} +//#enddef +#define STRTON(T, ...) STRTON__ ## T(__VA_ARGS__) I could actually fix the off-by-one attributes by moving the T to the end of the parameter list, and using the explicit parameter list here instead of ....

I would just write it as STRTON__ ## in the definition instead of using the STRTON macro, which would get rid fo the off-by-one. I also hides less of mechanism which I think is good. I also wonder whether you can replace the code in the c file with something such as extern inline typeof(STRTON__ ## uintmax_t) STRTON__ ## uintmax_t; instead of repeating all the arguments.

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[alejandro-colomar]

Am Montag, dem 10.03.2025 um 09:39 -0700 schrieb Alejandro Colomar:
I would just write it as STRTON__ ## in the definition instead of using the STRTON macro, which would get rid fo the off-by-one. I also hides less of mechanism which I think is good.

The good thing about using STRTON() is that it looks like a function definition. grepc(1) (my regex-based program for grepping C code) finds it just fine. However, if I use ##, then the regex doesn't find it.

I also wonder whether you can replace the code in the c file with something such as extern inline typeof(STRTON__ ## uintmax_t) STRTON__ ## uintmax_t; instead of repeating all the arguments.

I'm not too worried, since that repetition is checked by the compiler. Also, the same argument applied: regex-based programs will find the prototypes using STRTON().

https://www.alejandro-colomar.es/src/alx/alx/grepc.git/tree/bin/grepc

[alejandro-colomar]

Am Montag, dem 10.03.2025 um 09:39 -0700 schrieb Alejandro Colomar:
I would just write it as STRTON__ ## in the definition instead of using the STRTON macro, which would get rid fo the off-by-one. I also hides less of mechanism which I think is good.

The good thing about using STRTON() is that it looks like a function definition. grepc(1) (my regex-based program for grepping C code) finds it just fine. However, if I use ##, then the regex doesn't find it.

I also wonder whether you can replace the code in the c file with something such as extern inline typeof(STRTON__ ## uintmax_t) STRTON__ ## uintmax_t; instead of repeating all the arguments.

I'm not too worried, since that repetition is checked by the compiler. Also, the same argument applied: regex-based programs will find the prototypes using STRTON().

https://www.alejandro-colomar.es/src/alx/alx/grepc.git/tree/bin/grepc

@uecker

Actually, I correct myself. grepc(1) is able to grep the template definition with ## in its name as long as you include that in the search term.

$ grepc -h CMP .
#define CMP(T)  cmp__ ## T  // For use as a callback

$ grepc -hC1 'cmp__ ## T' .
#def template_cmp(T)
inline int
cmp__ ## T(const void *key, const void *elt)
{
	const T  *k = key;
	const T  *e = elt;

	if (*k < *e)
		return -1;
	if (*k > *e)
		return +1;
	return 0;
}
#enddef

So, I'll follow your suggestion and make it explicit that I'm using ## in the template definition. It will make the machinery more readable.

[alejandro-colomar]

I also wonder whether you can replace the code in the c file with something such as extern inline typeof(STRTON__ ## uintmax_t) STRTON__ ## uintmax_t; instead of repeating all the arguments.
…

No, you can't.

search/cmp/cmp.c:12:28: error: stray '##' in program
   12 | extern inline typeof(CMP__ ## int)     CMP__ ## int;
      |                            ^~
search/cmp/cmp.c:12:22: error: 'CMP__' undeclared here (not in a function); did you mean 'CMP'?
   12 | extern inline typeof(CMP__ ## int)     CMP__ ## int;
      |                      ^~~~~
      |                      CMP
search/cmp/cmp.c:12:27: error: expected ')' before 'int'
   12 | extern inline typeof(CMP__ ## int)     CMP__ ## int;
      |                     ~     ^   ~~~
      |                           )

Concatenation doesn't work outside of macros. I guess I'll either concatenate myself, or write a small macro for that.