问元数据注释中的Dart2js括号符号

EN

@MirrorsUsed(metaTargets: Tag)
import 'dart:mirrors';

class Tag {
  final Symbol name;
  const Tag(this.name);
}
@proxy
@Tag(#[])
class Tagged {
  noSuchMethod(Invocation invocation) {
    InstanceMirror instanceMirror = reflect(this);
    ClassMirror classMirror = instanceMirror.type;
    classMirror.metadata.forEach((em) {
      if (em.reflectee is Tag && em.reflectee.name == invocation.memberName)
         print(invocation.positionalArguments);
    });
  }
}
void main() {
  var tagged = new Tagged();
  tagged[42];
  tagged.foo();
  tagged["Dart"];
}