Extended Type Design.

[janderson]

Andrei Alexandrescu (See Website For Email) wrote:
> Bruno Medeiros wrote:
>> What is the status of the experimental designs for the "storage 
>> classes" manipulation that Andrei and others where thinking of for D. 
>> The last I heard from it was Andrei's max suggestion from his max 
>> design challenge, however, I think that suggestion may suffer from 
>> some problems in regards to the "maxtype" requirement, plus it is 
>> wholly incomplete in regards to how storage classes interact between 
>> each other. Like Andrei said, what is a "const inout lazy const 
>> char[]", if valid at all? Is there any news here? Is there a 
>> working(aka complete) design?
> 
> We have talked about a design. In short, the intent is to define three 
> flavors of immutability:
> 
> a) final - a simple storage class controlling the immutability of the 
> bits allocated for the symbol per se;
> 
> b) const - type qualifier meaning an immutable view of an otherwise 
> modifiable data. const does not control the bits of the object, only the 
> storage addressed indirectly by it (transitively);
> 
> c) "superconst" - denoted as "const!" or "super const": type qualifier 
> meaning that the data is genuinely unmodifiable.
> 
> There is talk about deprecating lazy if it's best implemented via other 
> mechanisms. There is also talk about deprecating "inout" in favor of 
> "ref" on grounds that the often-useful "inout const" is likely to become 
> #1 reason for bashing D.
> 
> To read a declaration like "const inout lazy const char[]", you can 
> first parenthesize it appropriately:
> 
> const(inout(lazy(const(char[]))))
> 
> The lazy thing is really a delegate that returns a const char[]. The 
> inout around it passes that delegate by reference, and the const at the 
> top makes the delegate immutable.
> 
> 
> Andrei


Thanks for the update:

BTW:

const!(char[])

Looks to much like a template to me, I'd imagine some syntax phasers 
would have a harder time then necessary.

-Joel