Why I am getting negative result for negativeValue.abs()?

I have an extension like;

extension x on num{}

and this extension contains below function;

double get wP {
assert(this >= 0.0, "value.wP: value can't be lower than 0.0!");
assert(this <= 1.0, "value.wP: value can't be bigger than 1.0!");
return (this.abs() * SizeService.instance.width).abs();}

SizeService.instance.width is a integer and it is = 50.

So, why -1.0.wp returning -50 ?

and I wan’t to block all negative variable like;
-0.0 too but if I write assert like

assert(!this.isNegative, "Error bla bla");

it is not catching the negative value 🙁

so my question is here;

how can I block all negative and nan variables or if I can’t do it, how can I convert all negative variables to positive ones ?

-0.0 is too.

because this.abs() is not working :/

thank u very much for any helpful answer!

>Solution :

-1.0.wP is in fact the same as -(1.0.wP)

Instead, try with (-1.0).wP