operator unary- method Null safety
The negation of this value.
The negation of a number is a number of the same kind
double) representing the negation of the
numbers numerical value (the result of subtracting the
number from zero), if that value exists.
Negating a double gives a number with the same magnitude
as the original value (
number.abs() == (-number).abs()),
and the opposite sign (
-(number.sign) == (-number).sign).
Negating an integer,
-number, is equivalent to subtracting
it from zero,
0 - number.
(Both properties generally also hold for the other type, but with a few edge case exceptions).
double operator -();