"alias that this" or "alias this : that"

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On Friday, 7 February 2014 at 07:36:57 UTC, Mike wrote:
> Can someone please clarify for me which of these is the 
> "preferred" syntax?
>
> alias that this;
> alias this : that;
>
> The documentation here (http://dlang.org/class.html#AliasThis) 
> doesn't mention the latter.  I'll do the unrewarding work of 
> updating the docs if someone could just please tell me which 
> syntax the core language folks prefer.
>
> Thanks.
> Mike
>
> For context:
> https://github.com/D-Programming-Language/dmd/pull/1413
> https://github.com/D-Programming-Language/dmd/pull/1685

`alias this : that` was discussed but has never been implemented, 
so currently the only way to do it is `alias that this`.