case子句与记录类型不匹配

本文介绍了case子句与记录类型不匹配的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

为什么 case 子句与记录类型不匹配?

Why doesn't the case clause match the record type?

(defrecord Rec []) => fargish.user.Rec (def rec (->Rec)) => #'fargish.user/rec (case (type rec) Rec :YES) => IllegalArgumentException No matching clause: class fargish.user.Rec fargish.user/eval25147 (form-init131856794870899934.clj:1)

如果您想知道，是的，case表达式和test-constant相等:

In case you're wondering, yes, the case expression and the test-constant are equal:

(= (type rec) Rec) => true

推荐答案

Rec 不是编译时文字.引用自 clojuredocs/clojure.core/case :

Rec is not a compile-time literal. Quoting from clojuredocs/clojure.core/case:

所有情况下的常量表达式都可以接受，包括数字，字符串，符号，关键字及其(Clojure)组合.

All manner of constant expressions are acceptable in case, including numbers, strings, symbols, keywords, and (Clojure) composites thereof.

替代品:

(cond (= (type rec) Rec) :YES) ;;=> :YES (condp = (type rec) Rec :YES) ;;=> :YES