Solving a constraint hiding an error in a function literal

[WebFreak001]

On Friday, 3 February 2023 at 13:57:02 UTC, Steven Schveighoffer 
wrote:
> On 2/3/23 7:43 AM, Nick Treleaven wrote:
>
>> if (__traits(callable, a, int()))
>
> GMTA?
>
> https://forum.dlang.org/post/rj5hok$c6q$1@digitalmars.com
>
> -Steve

I remember this thread now and I'm actually amazed we haven't 
been making any progress towards this yet, because this looks 
like such a simple and elegant solution we could use for new code 
and Phobos v2. (because it's a backwards incompatible change when 
suddenly other code paths would attempt to compile I think)

I'll try starting a DIP, maybe that's just everything we need to 
get going.