The in operator (along with other things) is designed poorly.

[Ruby The Roobster]

On Tuesday, 31 May 2022 at 00:52:30 UTC, Ruby The Roobster wrote:
> On Tuesday, 31 May 2022 at 00:48:57 UTC, Ruby The Roobster 
> wrote:
>> On Tuesday, 31 May 2022 at 00:16:46 UTC, Ruby The Roobster 
>> wrote:
>>...
>
> Nevermind.  This isn't a bug, and it isn't really an issue.

And what caused me to start writing the code that caused me to 
make this thread is the fact that interfaces only require the 
classes that inherit from them to implement virtual functions.  
This means that if you want to require classes that inherit from 
and interface to implement operator overloads, you can't rely on 
the compiler to do it for you:  you have to use __traits to make 
sure that those operator overloads exist.