return@map 的工作原理

Question

我刚刚开始使用 kotlin 学习 Java 流 API，并且我正在使用 Project Reactor 和 r2dbc API。我正在编写一个简单的代码，如下所示，如果理解它是如何工作的，我将不胜感激。

我想知道t.let{} 使用return@map 返回MovieCeleb 对象的行。我想知道这条线是做什么的，即它是否创建了一个列表/地图以及它是如何做到的。

fun listAllMoviesBy(actor: String, client: DatabaseClient) {
    client.execute()
            .sql { "SELECT fin.id, full_name, movie_title, make_year, celeb_id, birth_date " +
                    "FROM featured_in fin JOIN film_celeb fc ON " +
                    " fin.celeb_id = fc.id WHERE fc.full_name = $1"
            }.bind(0, actor).map { t, u ->
                t.let {
                   val featuredIn = FeaturedIn(it.get("id") as Int, it.get("movie_title") as String, it.get("make_year") as Int)
                   val celeb = MovieCeleb(it.get("celeb_id") as Int, it.get("full_name") as String, it.get("birth_date") as LocalDate, featuredIn)
                    return@map celeb
                }
            }.all()
            .subscribe{
                println(it)
            }
}

Answer 1

给定

.map { t, u ->
            t.let {
               val featuredIn = FeaturedIn(it.get("id") as Int, it.get("movie_title") as String, it.get("make_year") as Int)
               val celeb = MovieCeleb(it.get("celeb_id") as Int, it.get("full_name") as String, it.get("birth_date") as LocalDate, featuredIn)
                return@map celeb
            }
        }

return@map celeb 将从map 函数返回celeb 参考值（而不是来自let！）。它只是某种所谓的non-local return，而您可以手动指定语句的返回范围。