[RFC] Throwing an exception with null pointers

[Derek Fawcus]

On Wednesday, 16 April 2025 at 21:30:58 UTC, Richard (Rikki) 
Andrew Cattermole wrote:
> From a link made previously in this thread, the state of the 
> art annotation of nullability in C++: 
> https://clang.llvm.org/docs/analyzer/developer-docs/nullability.html

An example using it:

```C
// Compile with -Wnullable-to-nonnull-conversion

#if defined(__clang__)
	#define ASSUME_NONNULL_BEGIN _Pragma("clang assume_nonnull 
begin")
	#define ASSUME_NONNULL_END _Pragma("clang assume_nonnull end")
#else
	#define ASSUME_NONNULL_BEGIN
	#define ASSUME_NONNULL_END
	#define __has_feature(x) (0)
#endif /* clang */

#if __has_feature (nullability)
	#define NONNULL _Nonnull
	#define NULLABLE _Nullable
	#define NULL_UNSPECIFIED _Null_unspecified
#else
	#define NONNULL
	#define NULLABLE
	#define NULL_UNSPECIFIED
#endif /* nullability */

ASSUME_NONNULL_BEGIN

int *someNonNull(int *);
int *someNullable(int * NULLABLE);

int foo(int * arg1, int * NULL_UNSPECIFIED arg2, int * NULLABLE 
arg3) {
	int a = 0;
	int * NONNULL ptr;

	a += *someNullable(arg1);
	a += *someNullable(arg2);
	a += *someNullable(arg3);

	ptr = arg1;
	ptr = arg2;
	ptr = arg3;

	a += *someNonNull(arg1);
	a += *someNonNull(arg2);
	a += *someNonNull(arg3);

	return a;
}

ASSUME_NONNULL_END
```

```
$ clang-14 -Wall -Wnullable-to-nonnull-conversion -c ttt.c
ttt.c:37:8: warning: implicit conversion from nullable pointer 
'int * _Nullable' to non-nullable pointer type 'int * _Nonnull' 
[-Wnullable-to-nonnull-conversion]
         ptr = arg3;
               ^
ttt.c:41:20: warning: implicit conversion from nullable pointer 
'int * _Nullable' to non-nullable pointer type 'int * _Nonnull' 
[-Wnullable-to-nonnull-conversion]
         a += *someNonNull(arg3);
                           ^
ttt.c:29:16: warning: variable 'ptr' set but not used 
[-Wunused-but-set-variable]
         int * NONNULL ptr;
                       ^
3 warnings generated.
```