Negation of attributes (DIP 79)

[ref2401 via Digitalmars-d]

> This is by far not the only reason. It is just as well useful 
> for all other attributes: const, pure, @safe/@system, @nogc, 
> and maybe UDAs.
>
> It's long been recognized that a mechanism to switch off a 
> scope-wide attribute would be useful.

Switching attributes on and off will make your code more 
complicated. If one doesn't use scope-wide attributes much then 
he won't need to switch them off.