On 02/08/2012 07:30 PM, Artur Skawina wrote:
On 02/08/12 18:24, Timon Gehr wrote:
Open issue:
void main(){
unique x = new C;
pragma(msg, typeof(x.z)); // ???
auto y = x.z; // error?
immutable z = x;
}
x.z is not necessarily unique, but assigning it to y breaks the guarantees of
the unique qualifier of x.
This is why treating "unique" as a static storage class doesn't really work. One
of the two last lines above would have to be disallowed,
Actually that is not true. It could type check, because y is not alive
after x has been cast to immutable.
The problem shows here:
void main(){
unique x = new C;
auto y = x.z;
immutable z = x;
foo(y,z);
}
and that reduces its usefulness dramatically.
Can you show me an example of its use?
The "auto" assignment either has to be illegal, or
trigger a mutation, eg to immutable. I don't think having the compiler keep
track of all possible relations would be a practical solution, even if
theoretically
possible.
I think it would be practical enough.
typeof(C.z) global;
void main(){
unique x = new C;
auto y = x.z;
static assert(!is(typeof(y)==immutable));
static assert(!is(typeof({global = y;}));
immutable z = x;
static assert(is(typeof(y)==immutable));
static assert(is(typeof(x)==immutable);
foo(y,z);
}
For those not reading D.learn - unique helps in other cases too:
http://lists.puremagic.com/pipermail/digitalmars-d-learn/2012-February/029547.html
artur
