java - 检查 null 时惯用的 Kotlin

Question

在 Java 中，我会这样做:

class Person {

    private Record record;

    public String name() {
      record().get("name");
    }

    private Record record() {
      if (record == null) {
        refetch();
      }
      return record;
    }

    private void refetch() {
      record = service.doSomething()
    }

}

在 Kotlin 中，我有以下等效代码:

class Person(private var record: Record?) {

    fun name() : String {
      record().get("name");
    }

    private fun record() : Record {
      record ?: refetch()
      return record!!;
    }

    private fun refetch() {
      record = service.doSomething()
    }

}

如您所见，我正在使用 !! 运算符，但我不太喜欢。还有另一种更惯用的方法吗？

如果我简单地遵循 Java 方式 (if (record == null))，我会得到这个错误:

Smart cast to "Record" is impossible, because "record" is a mutable property that could have been changed by this time

Answer 1

在惯用的 Kotlin 中，您将使用 lazy delegated property :

class Person(private val service: Service) {

    private val record by lazy { service.doSomething() }

    fun name() = record.get("name");
}