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() => [year, month, day]
.notNull()
.map((part) => part < 10 ? "0$part" : "$part")
.join("-");