<script lang="ts">
import { ref, computed, reactive, toRefs } from "vue";
interface DataProps {
  count: number;
  double: number;
  increase: () => void;
  numbers: number[];
  person: { name?: string };
}
export default {
  name: "App",
  setup() {

    const data: DataProps = reactive({
      count: 0,
      increase: () => { data.count++ },
      double: computed(() => data.count * 2 ),
      numbers: [1, 2, 3],
      person: {}, //初始空对象
    });
    data.numbers[0] = 5; //第一项更新成5
    data.person.name = "Test";

    const refData = toRefs(data);

    return {
      ...refData,
    };
  },
};
</script>

请问，setup()函数里面的
double: computed(() => data.count * 2 )
加括号写成
double: computed(() => {data.count * 2} ),
就报错，而increase 后面的increase: () => { data.count++ }, 可以加大括号，这是什么原因呢