正在寻找reagent/atom
的行为的澄清。
这是《 Professional Clojure》第5章中的代码,运行无花果轮:
单位中的试剂版本为0.8.1
(ns whip.core
(:require [reagent.core :as reagent :refer [atom]]))
(defonce app-state
(reagent/atom
{:projects
{"aaa"
{:title "Build Whip"
:stories
{1 {:title "Design a data model for projects and stories"
:status "done"
:order 1}
2 {:title "Create a story title entry form"
:order 2}
3 {:title "Implement a way to finish stories"
:order 3}}}}}))
(defn project-board [app-state project-id]
(into [:ul]
(for [[id {:keys [title]}] (get-in @app-state [:projects project-id :stories])]
[:li title])))
在REPL上,如果我将取消引用的app-state
传递到项目板上,则会出现错误:
dev:whip.core=> (project-board @app-state "aaa")
#object[Error Error: No protocol method IDeref.-deref defined for type cljs.core/PersistentArrayMap: {:projects {"aaa" {:title "Build Whip", :stories {1 {:title "Design a data model for projects and stories", :status "done", :order 1}, 2 {:title "Create a story title entry form", :order 2}, 3 {:title "Implement a way to finish stories", :order 3}}}}}]
cljs.core/missing-protocol (jar:file:/Users/m/.m2/repository/org/clojure/clojurescript/1.10.520/clojurescript-1.10.520.jar!/cljs/core.cljs:316:4)
cljs.core/-deref (jar:file:/Users/m/.m2/repository/org/clojure/clojurescript/1.10.520/clojurescript-1.10.520.jar!/cljs/core.cljs:671:1)
cljs$core$deref (jar:file:/Users/m/.m2/repository/org/clojure/clojurescript/1.10.520/clojurescript-1.10.520.jar!/cljs/core.cljs:1452:4)
whip.core.project_board_reagentRender (file:/Users/m/clj-pro-clojure/code-and-notes/whip/src/whip/core.cljs:62:3)
但是如果我通过普通的var app-state
:
dev:whip.core=> (project-board app-state "aaa")
[:ul
[:li "Design a data model for projects and stories"]
[:li "Create a story title entry form"]
[:li "Implement a way to finish stories"]]
如果我在打印出副本时打印出普通var app-state
,则会打印出:
dev:whip.core=> app-state
#<Atom: {:projects {"aaa" {:title "Build Whip", :stories {1 {:title "Design a data model for projects and stories", :status "done", :order 1}, 2 {:title "Create a story title entry form", :order 2}, 3 {:title "Implement a way to finish stories", :order 3}}}}}>
如果我在repl中打印出解引用的var app-state
,它也会打印出来,但是现在语法缩进:
dev:whip.core=> @app-state
{:projects
{"aaa"
{:title "Build Whip",
:stories
{1
{:title "Design a data model for projects and stories",
:status "done",
:order 1},
2 {:title "Create a story title entry form", :order 2},
3 {:title "Implement a way to finish stories", :order 3}}}}}
为什么第一种情况失败?(如果某物是原子,我不应该期望总是取消引用它吗?)
在第一种情况下,您尝试两次deref
,因此失败了。
(project-board @app-state "aaa")
表示project-board
fn现在收到一个映射作为参数,而不是原子。因此(get-in @app-state ...)
失败,因为映射未实现deref
协议。
No protocol method IDeref.-deref defined for type cljs.core/PersistentArrayMap