multiple `alias this` suggestion

[Steven Schveighoffer via Digitalmars-d]

On 4/21/17 8:17 AM, Andrei Alexandrescu wrote:
> On 04/20/2017 04:35 PM, Carl Sturtivant wrote:
>> On Wednesday, 19 April 2017 at 18:32:43 UTC, Carl Sturtivant wrote:
>>> Imagine the existing single `alias this` is extended to provide such a
>>> heierarchy of lookups. For example,
>>>
>>> struct top
>>> {
>>>     mem3 m3;
>>>     mem2 m2;
>>>     mem1 m1;
>>>     alias m3, m2, m1 this;
>>>     // ...
>>> }
>>>
>>> could be interpreted to mean search for a name in m3 if not found in
>>> top, and in m2 if not found in m3 and in m1 if not found in m2. I
>>> don't back the syntax, just the notion.
>>>
>>> Maybe that's not all that's expected from "multiple alias this" but it
>>> would be a clean step forward. Issues?
>>
>> No issues then!
>> Time for a D I P perhaps.
>> Comment?
>
> This is interesting, and would be timely to discuss before an
> implementation of multiple alias this gets started. -- Andrei
>

I agree, I like how this solves the ambiguity problem nicely. However, 
this disallows using introspection to declare multiple alias this 
piecemeal. e.g.:

struct S(bool foo)
{
   int x;
   alias x this;
   static if(foo)
   {
      string y;
      alias y this;
   }
}

One thing we can do also is just use declaration order to prioritize 
which alias this to use.

-Steve