dart 类型提升

Object text = 'IAM17';
 if (text is String) {
   print(text.length);
 }
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class Person {
  String? get name => "IAM17";
  getNameLength() {
    if (name is String) {
      return name.length;
    }
  }
}
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String? get name => Random().nextBool() ? "IAM17" : null;
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class Person {
  String? get name => Random().nextBool() ? "IAM17" : null;
  getNameLength() {
    var tmpName = name;
    if (tmpName is String) {
      return tmpName.length;
    }
  }
}
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