OK,clear. But why would it still work for alpha<=0.37?

Probably undefined behavior that happened to work. It's usually best to avoid undefined behavior in the first place.

Just to understand: overloaded function resolution happens at compile time, and the sample code is 'deterministic' with respect to EMA(). Why would it then be 'undefined' behavior?


Btw: if the 2nd parameter is an int, rather than a var, all works fine...

At compile time, your function prototype is wrong. This is why you need a wrapper.

Ah, ok, tx!