Struct with default ctor (Was: [dmd-beta] dmd 2.064 beta take 2)

[Simen Kjaeraas]

On Sun, 19 May 2013 06:57:16 +0200, Walter Bright  
<newshound2 at digitalmars.com> wrote:

>> The current solution is to rely on faith, and I remember someone  
>> talking about
>> that at DConf recently.
>
> Rely on what faith?

void foo(int* p) {} // p must never be null
void foo(NotNull!(int*) p) {}

One of these is tested at compile time, *and* includes valuable
documentation in the signature. The other is either less performant
or buggy.


>> Now that what other languages does is cleared, let's do some  
>> consideration on null.
>>
>> A pointer point on something. For instance, an int* point on an  
>> integer. null
>> doesn't point on a integer. Non nullable pointer aren't a restricted  
>> set of
>> values, as, by definition, null isn't a value that point to an int.  
>> That doesn't
>> stand either.
>
> By definition? Pointer semantics are what we choose it to mean.

Of course. But which definition is saner:

   "T* is either a valid pointer to a T, or a value that blows up when used
   in certain ways (but not others)."

or

   "T* is a valid pointer to T."

Of course, the latter also requires something like Maybe!T:

   "Maybe!T is either a valid pointer to a T, or a value on which no
   operations may be performed. In order to gain access to the T, both
   cases have to be handled."

-- 
Simen