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

[mw]

On Wednesday, 19 October 2022 at 18:56:35 UTC, Paul Backus wrote:
> On Wednesday, 19 October 2022 at 18:38:55 UTC, mw wrote:
>
> It is possible to achieve both. If the compiler enforces the 
> rules I laid out in my initial post [1] (i.e., inheritance can 
> only remove @mustuse, not add it),

This won't work as Teoh has showed the loophole:

1) Base class has @mustuse, derived class does not.  Then the 
base class's @mustuse can be circumvented by a derived class that 
omits the attribute, defeating the purpose of @mustuse in the 
base class.


> Of course, this means that there will be some functions that 
> can never be marked as @mustuse without a breaking change--just 
> like with @safe and nothrow. But that's true even with your 
> proposal.

In any case it will be a breaking change, I never said otherwise; 
and it's not of my concern. My only concern is how to make the 
ideal D code more robust.