Worst ideas/features in programming languages?

[jmh530]

On Tuesday, 12 October 2021 at 19:41:57 UTC, H. S. Teoh wrote:
> [snip]
>> * Features you'd like to see in D
> [...]
>
> - C++ concepts-like feature of specifying the expected 
> interface of a
>   template parameter.
>    - Yes, sig constraints fit the bill, kinda-sorta.  But it 
> leads to
>      poor, unhelpful error messages.  Yes, this can be fixed by 
> using
>      static if, pragma(msg), etc., but this requires a lot of 
> extra work
>      on the part of the user which should have been handled by 
> the
>      language.
>    - Yes, there's a dub package that kinda-sorta does this. But 
> again,
>      this is something that should have been done by the 
> language.
>
> 

I've become more sympathetic to this. The main argument against 
DIP 1023 (resolution of template alias parameters in template 
functions) boiled down to "why not use signature constraints." 
Something like Concepts could be an alternative solution to the 
problems addressed in that DIP (though that may not be the only 
way to resolve them).

Runtime & static polymorphism comes in different types and 
flavors. D has class, which is similar to how C++ and Java work 
(ignoring some details). So we can group these together in a 
run-time polymorphism. D's interface is similar to that, but 
doesn't do exactly the same thing and is different from Go's 
interface and Rust's traits system. Concepts as a form of static 
polymorphism are in a different category as well. But how do we 
group the categories in a way that makes sense?