NonNull template

[kdevel]

On Saturday, 19 April 2025 at 22:23:54 UTC, Jonathan M Davis 
wrote:
>>
>>     int main ()
>>     {
>>        int *p = NULL;
>>        int &i = *p;
>>     }
>>
>> That is an error (mistake) only in C++ because the reference 
>> is not initialized with a valid initializer. In D, however,
>>
>>     void main ()
>>     {
>>        int *p = null;
>>        ref int i = *p; // DMD v2.111.0
>>     }
>>
>> is a valid program [3].
>
> In both cases it's a valid program

Only the D version is valid. The C++ program violates the std.
 From the SO page there is a quote of the C++ 11 std draft which
says in sec. "8.3.2 References":

     "A reference shall be initialized to refer to a valid object
      or function. [ Note: in particular, a null reference cannot
      exist in a well-defined program, because the only way to 
create
      such a reference would be to bind it to the “object” obtained
      by dereferencing a null pointer, which causes undefined 
behavior.
      [...] — end note ]"

You find nearly the same wording in sec. 11.3.2 of the C++17 std
draft (N4713) and in sec. 9.3.4.3 of the C++23 std draft (N4928)
with the "dereferencing" replaced with "indirection".

> [...] If it weren't a valid program, it wouldn't compile.

That is an interesting opinion.