让我们看一下 Clojure 规范指南中给出的示例clojure.spec/merge
(require '[clojure.spec :as spec]
'[clojure.spec.gen :as gen])
(spec/def :animal/kind string?)
(spec/def :animal/says string?)
(spec/def :animal/common (spec/keys :req [:animal/kind :animal/says]))
(spec/def :dog/tail? boolean?)
(spec/def :dog/breed string?)
(spec/def :animal/dog (spec/merge :animal/common
(spec/keys :req [:dog/tail? :dog/breed])))
根据这个规范,我们既可以生成数据,又可以验证它:
(gen/generate (spec/gen :animal/dog))
=> {:animal/kind "bB", :animal/says "z9C0T465Q8OPXn5dUB8Wqk8K5Jnn",
:dog/tail? false, :dog/breed "B2MLQnj"}
(spec/valid? :animal/dog
{:animal/kind "bB", :animal/says "z9C0T465Q8OPXn5dUB8Wqk8K5Jnn",
:dog/tail? false, :dog/breed "B2MLQnj"})
=> true
但是,如果我们要稍微修改规范,使其用于一系列命名参数而不是映射,例如
(spec/def :animal/common (spec/keys* :req [:animal/kind :animal/says]))
(spec/def :animal/dog (spec/merge :animal/common
(spec/keys* :req [:dog/tail? :dog/breed])))
,我们仍然可以根据规范验证数据:
(spec/valid? :animal/dog
'(:animal/kind "dog"
:animal/says "woof"
:dog/tail? true
:dog/breed "retriever"))
=> true
但是我们确实失去了生成数据的能力:
(gen/generate (spec/gen :animal/dog))
; 1. Unhandled clojure.lang.ExceptionInfo
; Couldn't satisfy such-that predicate after 100 tries.
这是我这边的错误,规范中的实现错误,或者只是clojure.spec/merge
打算工作的方式?我们可以通过附加发电机来解决这个问题吗?