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() {
  final params = namedProps.entries
      .map((e) =>
          hasValue(e.value) ? '${e.key}:${_formatPrint(e.value)}' : null)
      .where((o) => o != null)
      .join(', ');
  return '$runtimeType($params)';
}