Custom module behavior with custom in-line SystemVerilog representation

Many of the basic built-in gates in Dart implement custom behavior. An implementation of the NotGate is shown below as an example. There is different syntax for functions which can be inlined versus those which cannot (the ~ can be inlined). In this case, the InlineSystemVerilog mixin is used, but if it were not inlineable, you could use the SystemVerilog mixin instead. Note that it is mandatory to provide an initial value computation when the module is first created for non-sequential modules.

/// A gate [Module] that performs bit-wise inversion.
class NotGate extends Module with InlineSystemVerilog {
  /// Name for the input of this inverter.
  late final String _inName;

  /// Name for the output of this inverter.
  late final String _outName;

  /// The input to this [NotGate].
  late final Logic _in = input(_inName);

  /// The output of this [NotGate].
  late final Logic out = output(_outName);

  /// Constructs a [NotGate] with [in_] as its input.
  ///
  /// You can optionally set [name] to name this [Module].
  NotGate(Logic in_, {super.name = 'not'}) {
    _inName = Naming.unpreferredName(in_.name);
    _outName = Naming.unpreferredName('${in_.name}_b');
    addInput(_inName, in_, width: in_.width);
    addOutput(_outName, width: in_.width);
    _setup();
  }

  /// Performs setup steps for custom functional behavior.
  void _setup() {
    _execute(); // for initial values
    _in.glitch.listen((args) {
      _execute();
    });
  }

  /// Executes the functional behavior of this gate.
  void _execute() {
    out.put(~_in.value);
  }

  @override
  String inlineVerilog(Map<String, String> inputs) {
    assert(inputs.length == 1, 'Gate has exactly one input.');

    final a = inputs[_inName]!;
    return '~$a';
  }
}