Extended Type Design.

[kris]

Andrei Alexandrescu (See Website For Email) wrote:
> Daniel Keep wrote:
> 
>> This is fantastic news.  I'm really happy to know you guys are making
>> progress on this.
> 
> 
> Thank you! In fact, it did take an embarrassingly long time to implement 
> something within all of the self-imposed constraints, but now we're 
> really happy with the result.
> 
>> So if I understand this right:
>>
>> * "final int*" is an immutable pointer that points to mutable data,
> 
> 
> Yes. For example:
> 
> int a, b;
> final int * p = &a;
> *p = 5; // fine
> p = &b; // error! Cannot rebind final symbol!
> 
>> * "const int*" is a mutable pointer to immutable data, but that data
>> *may* be mutable in another context (ie: const((new int[10]).ptr)) and
> 
> 
> Exactly. For example:
> 
> int a;
> const int * p = &a;
> *p = 5; // error! Cannot modify const data!
> a = 5; // yah, modify data under the feet of p
> 
> This is a great feature for calling functions and providing "isolated" 
> interfaces. For example, say you write a function
> 
> void print(char[]);
> 
> You want to clarify to the caller that you NEVER modify their data. So 
> you define the function as:
> 
> void print(const char[]);
> 
> Then callers can call print with mutable or immutable data; it makes no 
> difference to print.
> 
> Unlike in C++, it takes much more effort to cast away constness, and the 
> results are never well-defined.
> 
>> * "const! int*" means "seriously, this *will not* change".
> 
> 
> Right. For example:
> 
> int a;
> const! int* p = &a; // error! cannot convert int* to const! int*
> final int b = 42;
> const! int* p1 = &b; // yah, b is truly immutable
> const! int* p2 = new const! int; // yah
> 
> 
> 
> Andrei


... and return values: "const char[] immutableTextProp()" ?

Just a thought on the const! syntax; it looks somewhat odd, and perhaps 
too much like template syntax?  How about calling one of the "const" 
types "readonly" or "view" instead?