I can't get Contravariant function args

In C++ I'm having a hell of time getting these new contravariant function parameters working.

>>5
How the hell do you write a web store without side-effects?

(side-effectless programming is the only advantage of Lisp as it allows scripts to run in no time at all, by simply not running them, I can see why some lazy programmers like Lisp, they don't even have to write the code at all, hahaha oh wow)