invariant/const class storage class

[Simen Kjaeraas]

On Thu, 02 Oct 2008 03:54:02 +0200, Andrei Alexandrescu  
<SeeWebsiteForEmail at erdani.org> wrote:

> Simen Kjaeraas wrote:
>> On Thu, 02 Oct 2008 03:46:00 +0200, Andrei Alexandrescu  
>> <SeeWebsiteForEmail at erdani.org> wrote:
>>
>>> Simen Kjaeraas wrote:
>>>> On Wed, 01 Oct 2008 16:23:32 +0200, Yigal Chripun  
>>>> <yigal100 at gmail.com> wrote:
>>>>
>>>>> Andrei Alexandrescu wrote:
>>>>>> Yigal Chripun wrote:
>>>>>>> Walter Bright wrote:
>>>>>>>> Simen Kjaeraas wrote:
>>>>>>>>> Is this really correct behavior? How then are we supposed to
>>>>>>>>> initialize our
>>>>>>>>> invariant objects?
>>>>>>>> Currently, create them as mutable ones, then cast them to  
>>>>>>>> invariant.
>>>>>>>
>>>>>>> I understand casting as breaking the type system. shouldn't there  
>>>>>>> be a
>>>>>>> way to create invariant objects without the cast?
>>>>>>> an invariant constructor seems a good way to solve this. any plans  
>>>>>>> on
>>>>>>> adding such a feature to D2?
>>>>>>
>>>>>> There are plans.
>>>>>>
>>>>>>> I think it can work like this:
>>>>>>>
>>>>>>> class A {
>>>>>>>   this(params) {}   // [1]
>>>>>>>   invariant this(params) {}  // [2]
>>>>>>> }
>>>>>>>
>>>>>>> // create a mutable object - will use type [1] c-tors.
>>>>>>> auto a = new A(params);
>>>>>>>
>>>>>>> // create an invariant object - will use type [2] c-tors.
>>>>>>> invariant a = new A(params);
>>>>>>>
>>>>>>> // create a const object - will use type [1] or [2] c-tors.
>>>>>>> const a = new A(params);
>>>>>>>
>>>>>>> in the const case, if there are two c-tors which only differ by
>>>>>>> invariant-ness of the c-tor using either will create ambiguity and
>>>>>>> therefore should be a compile-time error.
>>>>>>
>>>>>> Way, way, way more complicated than this.
>>>>>>
>>>>>> Andrei
>>>>>
>>>>> May I ask what are the complications?
>>>>  "Mortis Portalis Tackulatum - and he's still breathing"...
>>>
>>> Tackulatum? Was that tacitum?
>>>
>>> Andrei
>>>
>>   From Terry Pratchett's 'Pyramids'.
>>  Doctor: "Fairly straightforward. A case of mortis portalis tackulatum  
>> with complications."
>> Chidder: "What's that mean?"
>> Doctor: "In laymen's terms, he's as dead as a doornail."
>> Chidder: "What are the complications?"
>> Doctor: "He's still breathing."
>
> Heh. Funny, but what's the link?
>
> Andrei

Uhm, nothing really. Just this managed to slip past my nonsense filter at  
4 in the morning.

-- 
Simen