> This doesn't make any sense.  Once you've exposed an API that gives
> out a value for this, you can't change the implementation in a way
> that doesn't involve handing out a value... in which case you can just
> as easily set it as an attribute.

Because it may be computed whenever the function call is done, rather
than stored statically somewhere. The caching scheme will not
necessarily remain forever identical.

> If there
> must be a way to change it later to be dynamic, it can always be
> exposed as an attribute of an object that could grow a property later,
> e.g.

That's a possibility indeed.