invariant/const class storage class

[Yigal Chripun]

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?