callable.dart

// ignore_for_file: unused_local_variable, unused_field

class MyCallable<TParam, TReturn> {
  final TReturn _defaultValue;

  MyCallable(this._defaultValue);

  TReturn call([TParam? value]) {
    if (value != null) {
      print('MyCallable instance called with parameter: $value');
    } else {
      print('MyCallable instance called without parameter');
    }
    return _defaultValue;
  }
}

class Processor<R1, R2> {
  final R1 Function()? _callbackWithoutParam;
  final void Function() voidCallback;
  final void Function()? nullableCallBack;
  final void Function()? nullableCallBack2;

  Processor({
    R1 Function()? callbackWithoutParam,
    this.nullableCallBack,
    this.nullableCallBack2,
    required this.voidCallback
      
  })  : _callbackWithoutParam = callbackWithoutParam;

}

void main() {
  var callable = MyCallable<String, String>('Default string result');
  var callableNoParamVoid = MyCallable<void, void>('Default string result');
  
  bool isActive=true;
  
  final handler = isActive ? callableNoParamVoid : null;
 
  Processor<String, bool>(
    callbackWithoutParam: callable,
    voidCallback: callable,
    nullableCallBack: callableNoParamVoid,
    nullableCallBack2: handler
  );

}