toString method
A string representation of this object.
Some classes have a default textual representation,
often paired with a static parse function (like int.parse).
These classes will provide the textual representation as
their string representation.
Other classes have no meaningful textual representation
that a program will care about.
Such classes will typically override toString to provide
useful information when inspecting the object,
mainly for debugging or logging.
Implementation
@override
String toString() {
if (exponent == 0) return '$amount $currency';
final int unit = _pow10(exponent);
final String minor =
(amount % unit).toString().padLeft(exponent, '0');
return '${amount ~/ unit}.$minor $currency';
}