DIP66 v1.1 (Multiple) alias this.

[IgorStepanov via Digitalmars-d]

On Monday, 3 November 2014 at 20:06:27 UTC, Marc Schütz wrote:
> On Monday, 3 November 2014 at 15:39:42 UTC, IgorStepanov wrote:
>> I meant that when you say that X is a subtype of T and X is a 
>> subtype of V where you don't know what T and V are, it means 
>> you don't really know what you're doing. And that is an error 
>> and the compiler should inform you about it as soon as 
>> possible. However I may be mistaken.
>
> IMO the behaviour should be analogous to name lookup for 
> modules: there should be an error only on use. It's hard to 
> come up with a non-artificial example, but I can imagine there 
> are some valid use cases in generic code. It won't hurt to 
> report the ambiguity error on use, while it could theoretically 
> hurt to report it early, so I'd suggest to go with the former.

There are two cases:
1: when "alias a this" tries to override base class typeof(a)
2: when "alias a this" tries to override "alias b this" where 
"is(typeof(a) == typeof(b))"

The first check is hard to implement at lookup-time, because base 
classes are resolved before alias this.
The second check may be easely dropped (anyway alias this 
conflicts are resolved properly at lookup time).

Do you accept this scheme (remove the second check but still 
alive the first check)?