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

[Walter Bright]

On 5/18/2013 5:04 PM, deadalnix wrote:
> On Saturday, 18 May 2013 at 20:59:41 UTC, Simen Kjaeraas wrote:
>> @disable this is awesome, really. And you're right that it's even better than
>> simple non-nullable pointers. Lastly, it's great that it's getting fixes. It's
>> been one of my favorite non-working features. :p
>>
>
> The subject here is default constructor, not really nullable pointer. @disable
> this() cost as much as default constructor, but provide less. I don't see any
> objective reason to limit default constructor as disabled but not enabled.
>
> I'd even argue that it actually cost more as it introduce yet another special case.

     this() { assert(0); }

makes for a runtime check, not a compile time one. Compile time checks are more 
efficient in both programmer time and run time.

Note that C++11 8.4.3 has @disable as well, in the form:

    S() = delete;

>> In a way, I fear that we'll end up like C++, with bare pointers/references
>> being considered experts-only and 'special use', and everyone will use smart
>> pointers instead.
>
> No what will happen it that we will have null all over the place with missing
> check, and no stack trace when it fails, because NullPointerError have been
> decided to be bad.
>
> regular references/pointer are used way more than in C++ because you don't need
> to do the manual memory management that goes with it in D.
>
> We will have more bugs and slower programs due to null checks all over the
> place, and unexpressed assumption about what can be null and what cannot.

With NotNull, the runtime check only happens upon assignment and initialization 
from a pointer type. Dereferencing, copying, etc., of NotNull entails zero 
runtime overhead and no checks.