invariant/const class storage class

[Andrei Alexandrescu]

Simen Kjaeraas wrote:
> 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.

I kept on thinking of connections const/invariant -> rigor mortis.

Andrei