Returns the integer double value closest to this.
Rounds away from zero when there is no closest integer: (3.5).roundToDouble() == 4 and (-3.5).roundToDouble() == -4.
If this is already an integer valued double, including -0.0, or it is not a finite value, the value is returned unmodified.
For the purpose of rounding, -0.0 is considered to be below 0.0, and -0.0 is therefore considered closer to negative numbers than 0.0. This means that for a value, d in the range -0.5 < d < 0.0, the result is -0.0.
double roundToDouble();
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https://api.dart.dev/stable/2.5.0/dart-core/double/roundToDouble.html