DIP66 - Multiple alias this

[IgorStepanov via Digitalmars-d]

On Monday, 13 October 2014 at 15:21:32 UTC, Daniel N wrote:
>>>> On 10/11/2014 7:23 AM, IgorStepanov wrote:
>>>>> class A
>>>>> {
>>>>> int i;
>>>>> alias i this;
>>>>> }
>>>>>
>>>>> class B
>>>>> {
>>>>> int i;
>>>>> alias i this;
>>>>> }
>>>>>
>>>>> class C
>>>>> {
>>>>> A a;
>>>>> B b;
>>>>> alias a this;
>>>>> alias b this;
>>>>> }
>
> My preferred solution would be to reject the 2nd alias 
> declaration outright.
>
> I don't see any value in intentionally creating the above 
> pattern, _if_ it occurs then it's most likely due to an 
> unintentional side-effect of a re-factoring, thus it should 
> error out as close as possible to the real error.

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.