因为map接受一个参数，即一个函数，我们可以用_占位符来替代有名参数。
Because map takes one argument, a function, we can use the "placeholder" indicator _ instead of a named parameter.
注解还可以接受命名元素(named element)，这种元素与方法参数相似，但是参数的次序和数量不重要，因为每个参数都有名称。
Annotations can also take named elements, which are similar to method parameters, except that the parameters' order and number don't matter because each one is named.
其他增强包括call语句能够以任意次序接受有名称的参数。
Other enhancements include the ability for CALL statements to take named arguments in any order.
应用推荐