Reimplementing the bulk of std.meta iteratively

[Bruce Carneal]

On Thursday, 1 October 2020 at 01:49:02 UTC, Andrei Alexandrescu 
wrote:
> On 9/30/20 7:36 PM, H. S. Teoh wrote:
>> I think there's a lot of value to be had in making typeid(T) 
>> as the
>> reification of T.  At compile-time, we treat it specially by 
>> augmenting
>> it with the ability to do things that can only be done at 
>> compile-time,
>> such as recover T given typeid(T) (pass it into a template 
>> parameter,
>> construct new types out of it, etc.). At runtime, it reverts 
>> to the
>> current behaviour of typeid(T).
>> 
>> Only trouble is, according to Andrei, typeid has been written 
>> over so
>> many times that even Walter doesn't understand how it works 
>> anymore.
>> Meaning there are probably weird corner cases and quirky 
>> behaviours that
>> we may not want to duplicate at compile-time. So I dunno, this 
>> seems
>> like a roadblock to further progress.
>
> Yah, that would be my favorite by far. It's a one-liner change 
> in the definition of the language. "Since version x.xx, the 
> result of typeid() is usable during compilation." It's also the 
> best /kind/ of change to the language, i.e. lifts a gratuitous 
> restriction that prevents composition of distinct features 
> (here, ctfe and typeid).
>
> A promising path according to Walter is to develop a parallel 
> enhanced feature - newtypeid! :o) - and then deprecate typeid.

Glad to see that you're open to changing the language in order to 
achieve better power/complexity ratio.  Right there with you on 
that sentiment!

Two questions:

1) How many additional additions do you estimate you'll need for 
this? and

2) How do the type function addition(s) compare?  Are they also 
of the "best kind of change" variety?