Command–query separation principle [re: @mustuse as a function attribute]

[mw]

On Wednesday, 19 October 2022 at 08:29:20 UTC, mw wrote:
> OK, I saw what they are talking about.
>
>
> Basically, in Eiffel, all query @mustuse.
>
> Here in D @mustuse is an remedy add-on, which can be specified 
> by the programmers in the middle of the inheritance tree, the 
> question is what if the pointers got casted either upwards or 
> downwards?
>
> (It's too late for me here today.)
>

My gut feeling is: make it simple, if a method is marked as 
@mustuse anywhere in the inheritance tree, that method in all the 
class levels of the inheritance tree became @mustuse!