On Wednesday, 15 October 2014 at 02:46:05 UTC, Dicebot wrote:
On Tuesday, 14 October 2014 at 12:33:50 UTC, IgorStepanov wrote:
This code tell that C is subtype of A and C is subtype of B.
User can use this fact in his code:
void foo(B);
C c = new C;
foo(c); //Ok.
Of course, we shouldn't allow user to cast c to int:
int i = c; //wrong
However, user can explicitly cast c to his subtype, which is
convertable to int:
int i = cast(B)c; //Ok
Summarizing, I disagree with suggestion disallow this code at
type semantic stage.
I agree. It will also make possible to break already working
disambugation of `foo(c)` kind but adding new `alias this` to
one of subtypes independently. That sounds annoying.
I guess the best part of D is, you have the means to fix anything
you disagree with yourself... I can add a static assert to my
class and be happy.
I have another idea, we could define that the shortest conversion
chain wins, analogous to type promotions, that makes it possible
to contain the issue inside C.
class C
{
A a;
B b;
int disambiguate_int()
{
return a;
}
alias a this;
alias b this;
alias disambiguate_int this;
static assert(__traits(compiles, {int _ = C.init;}), "Ambiguous
alias this");
}
i.e. this assert should pass.
