dart 开发：avoid control flow in finally blocks.

带返回值的函数，如果抛出异常，那么返回值该如何处理呢？最常见的错误是：avoid control flow in finally blocks.

void main() {
  int result = tryCatch();
  print(result);
}
int tryCatch(){
  try {
    print("try...");
    throw "this is exception";
    return 1; //无效代码，因为上句已经抛出异常，不再执行此行代码
  } catch (e) {
    print("catch...");
    // return 2; //返回值的正确位置
  } finally {
    print("finally...");
    // return 3; //如果在此处返回函数值，则会有提示：avoid control flow in finally blocks.
  }
}