Multiple alias this, what's the hold up?

[Timon Gehr]

On 16.06.19 03:04, Jonathan Marler wrote:
> On Saturday, 15 June 2019 at 23:30:09 UTC, 12345swordy wrote:
>> On Saturday, 15 June 2019 at 10:12:46 UTC, Amex wrote:
>>> How many years has it been in limbo? 1? 2? 3? 5? 10?
>>>
>>> What is the hold up?
>>
>> What the hold up is that walter thinks it is a bad idea to implement 
>> multiple alias this as he think it results in a multiple inheritance 
>> problem. There has been recent discussion regarding deprecating alias 
>> this.
> 
> Maybe we could add it as an optional feature enabled with a command-line 
> option?
> 
> I think there's a command line format for features like this 
> "-feature=miltialias" or something.
> ...

That probably won't fly.

> That way if there really are issues we could demonstrate them and remove 
> the feature later, or if no issues are found it could be enabled by 
> default.

In terms of lookup, the issues with multiple alias this are the same as 
the issues with multiple import declarations. Implicit conversions could 
use the same lookup rules, but there would need to be a way to 
disambiguate. The code in the compiler that implements import 
declarations is unlikely to be easily reusable.