multiple `alias this` suggestion

[Meta via Digitalmars-d]

On Thursday, 20 April 2017 at 20:35:04 UTC, 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?

auto x = top(1,2,3);

void takesMember1(member1) {}
void takesMember2(member2) {}
void takesMember3(member3) {}

static assert(__traits(compiles, { takesMember1(x); }));  //Passes
static assert(__traits(compiles, { takesMember2(x); })); //Passes
static assert(__traits(compiles, { takesMember3(x); })); //Passes

This is a little bit surprising until you think about it a bit. 
It's also how we would want multiple alias this to behave were it 
implemented, which is a plus.