Multiple alias this, what's the hold up?

[user1234]

On Monday, 17 June 2019 at 13:48:45 UTC, Mike Franklin wrote:
> I think if we had an `opAssignRight` feature (with friends) we 
> could move the entire implementation of `alias this` to the 
> library. [...]
> Mike

At first glance opAssignRight is a really **brilliant** idea 👍.
Why do you think that variants would be required ? i += s would 
work with the single op overload. Maybe it would more be 
something like

T opExtractRight(T){}, with T saying what type is involved in the 
operation

int i = s  rewritten as  int i = s.opExtractRight!int();
i += s     rewritten as  i += s.opExtractRight!int();