DIP66 - Multiple alias this

[12345swordy]

On Monday, 28 September 2020 at 19:55:10 UTC, Andrei Alexandrescu 
wrote:
> On 9/28/20 2:44 PM, H. S. Teoh wrote:
>> On Mon, Sep 28, 2020 at 06:28:05PM +0000, mw via Digitalmars-d 
>> wrote:
>>> On Monday, 28 September 2020 at 18:13:15 UTC, H. S. Teoh 
>>> wrote:
>>>> On Mon, Sep 28, 2020 at 05:59:19PM +0000, mw via 
>>>> Digitalmars-d wrote:
>>>>
>>>> As somebody already said, that's all well and good for 
>>>> Eiffel. It's
>>>> not so clear how to integrate this nicely in D.
>>>
>>> D has `alias` already,
>> [...]
>> 
>> `alias this` is one of the things that seemed like a good idea 
>> at the
>> time, but is turning out to be something that leads to code 
>> smells.  If
>> anything, we'd like to get rid of it rather than extend it!
>
> I'd love to get a better idea about this, e.g. a few clear 
> examples of bad uses and other few good examples where it's a 
> win. My intuition vaguely revolves around "aliasing to an 
> rvalue is bad and lvalue is good" but I year for clarity.

An example of bad use is when you "alias this" a class inside a 
class. A good case is when you "alias this" a struct inside a 
struct.

An ideal case for me is allowing classes to implement opimplicit 
that strictly returns a copy of a value type, so that we can get 
rid alias this for classes.

-Alex