`restricted` member variables

[Mike Parker]

On Monday, 20 June 2022 at 11:16:40 UTC, deadalnix wrote:

> The simple way out of this is that, if it touches thee class's 
> privates parts, it ought to run the invariant checks.

That was my first thought. But then there's the case of the 
function contracts. That's what led me to this.

If my only invariant is the state of a single member variable, 
then I really only want it checked on the function(s) that 
actually write to it.