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Generalize const_cast(), and use it more. #1374

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Generalize const_cast(), and use it more. #1374

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6c5402f
lib/cast.h: const_cast(): Pass through other types
alejandro-colomar Oct 18, 2025
facb44c
lib/atoi/a2i.h: Use const_cast() instead of a raw cast
alejandro-colomar Oct 18, 2025
aa4a07b
lib/string/: Use QChar_of() to simplify some macros
alejandro-colomar Nov 25, 2025
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3 changes: 2 additions & 1 deletion lib/atoi/a2i.h
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Original file line number Diff line number Diff line change
Expand Up @@ -13,6 +13,7 @@

#include "atoi/strtoi/strtoi.h"
#include "atoi/strtoi/strtou_noneg.h"
#include "cast.h"
#include "typetraits.h"


Expand All @@ -35,7 +36,7 @@
unsigned int: strtou_noneg, \
unsigned long: strtou_noneg, \
unsigned long long: strtou_noneg \
)(s, (char **) endp_, base, min_, max_, &status); \
)(s, const_cast(char **, endp_), base, min_, max_, &status); \
\
if (status != 0) \
errno = status; \
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2 changes: 1 addition & 1 deletion lib/cast.h
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Expand Up @@ -9,7 +9,7 @@
#include "config.h"


#define const_cast(T, p) _Generic(p, const T: (T) (p))
#define const_cast(T, p) _Generic(p, const T: (T) (p), default: (p))

@kees kees Feb 26, 2026

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A down-side of this change is that if T is ever already const-qualified, this code will fail to build (on at least Clang), as const const ... is not a valid type qualifier. The original _Generic() macros handled this by matching const with a pass-thru, and only adding const when it was missing.

@alejandro-colomar alejandro-colomar Feb 26, 2026 •
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@kees

$ git log --pretty=reference lib/cast.h
eb71706b (*/: Fix including <config.h> as system header, 2025-07-15)
69f74dbf (lib/cast.h: const_cast(): Reimplement with _Generic(3), 2024-05-15)
e9fc8fc7 (lib/cast.h: const_cast(): Add macro for dropping 'const', 2024-01-07)

By "the original _Generic() macros" you mean this, right?

$ git show 69f74dbf:lib/cast.h | grepc -h const_cast
#define const_cast(T, p)  _Generic(p, const T:  (T) (p))

69f74db (2024-06-04; "lib/cast.h: const_cast(): Reimplement with _Generic(3)")

I think that would also fail for const char *, as it would expand const T as const const char *, right?



#endif // include guard
18 changes: 5 additions & 13 deletions lib/string/strcmp/strcaseprefix.h
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Expand Up @@ -13,22 +13,14 @@

#include "attr.h"
#include "cast.h"
#include "typetraits.h"


// string case-insensitive prefix
// strcaseprefix - string case-insensitive prefix
#define strcaseprefix(s, prefix) \
({ \
const char *p_; \
\
p_ = strcaseprefix_(s, prefix); \
\
_Generic(s, \
const char *: p_, \
const void *: p_, \
char *: const_cast(char *, p_), \
void *: const_cast(char *, p_) \
); \
})
( \
const_cast(QChar_of(s) *, strcaseprefix_(s, prefix)) \
)


ATTR_STRING(1) ATTR_STRING(2)
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18 changes: 5 additions & 13 deletions lib/string/strcmp/strprefix.h
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Expand Up @@ -13,22 +13,14 @@

#include "attr.h"
#include "cast.h"
#include "typetraits.h"


// string prefix
// strprefix - string prefix
#define strprefix(s, prefix) \
({ \
const char *p_; \
\
p_ = strprefix_(s, prefix); \
\
_Generic(s, \
const char *: p_, \
const void *: p_, \
char *: const_cast(char *, p_), \
void *: const_cast(char *, p_) \
); \
})
( \
const_cast(QChar_of(s) *, strprefix_(s, prefix)) \
)


ATTR_STRING(1)
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