关于关键字参数的抽象

Question

h2. 问题

如果两个函数接受相似的关键字参数，我们必须写出两次。


(ann make-contract [& :optional {:name (U Symbol String)
                                 :first-order [Any :-> Any]
                                 :projection [Blame :-> [Any :-> Any]]
                                 :flat? Boolean}
                    :-> Contract])

(ann make-flat-contract [& :optional {:name (U Symbol String)
                                 :first-order [Any :-> Any]
                                 :projection [Blame :-> [Any :-> Any]]
                                 :flat? Boolean}
                    :-> Contract])


由于HMap语法非常相似，并且关键字参数经常流入HMap类型，所以最好将这些指定为HMap类型。


(defalias KW
  (HMap :optional {:name (U Symbol String)
                   :first-order [Any :-> Any]
                   :projection [Blame :-> [Any :-> Any]]
                   :flat? Boolean}))
(ann make-contract [& :HMap KW :-> Contract])

(ann make-flat-contract [& :HMap KW :-> Contract])


h2. 问题

HMap的并集意味着什么？

例如。

(defalias KW
  (U '{:a Int}
     '{:b Int}))
(ann make-contract [& :HMap KW :-> Contract])


nil代表什么？


(defalias KW
  (U '{:a Int}
     nil))
(ann make-contract [& :HMap KW :-> Contract])

Answer 1

参考：https://clojure.atlassian.net/browse/CTYP-301（由ambrosebs报告）