Add koan for metadata

This commit is contained in:
Bryant 2015-07-12 13:03:34 -07:00
parent b1ea905c57
commit 173dd560d7
2 changed files with 61 additions and 0 deletions

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@ -219,4 +219,14 @@
{:naughty-list [{:name "Jimmy" :bad true}
{:name "Joe" :bad true}]
:nice-list [{:name "Jane" :bad false}]}]}]
["22_meta" {"__" [{:league "National League"}
{:division "West"}
"This doesn't implement the IObj interface"
{:foo :bar}
nil
\C
inc
:park "AT&T Park"
'Giants
"Giants"]}]
]

51
src/koans/22_meta.clj Normal file
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@ -0,0 +1,51 @@
(ns koans.22-meta
(:require [koan-engine.core :refer :all]))
(def giants
(with-meta 'Giants
{:league "National League"}))
(meditations
"Some objects can be tagged using the with-meta function"
(= __ (meta giants))
"Or more succintly with a reader macro"
(= __ (meta '^{:division "West"} Giants))
"While others can't"
(= __ (try
(with-meta
2
{:prime true})
(catch ClassCastException e
"This doesn't implement the IObj interface")))
"Notice when metadata carries over"
(= __ (meta (merge '^{:foo :bar} {:a 1 :b 2}
{:b 3 :c 4})))
"And when it doesn't"
(= __ (meta (merge {:a 1 :b 2}
'^{:foo :bar} {:b 3 :c 4})))
"Metadata can be used as a type hint to avoid reflection during runtime"
(= __ (#(.charAt ^String % 0) "Cast me"))
"You can directly update an object's metadata"
(= 8 (let [giants
(with-meta
'Giants
{:world-series-titles (atom 7)})]
(swap! (:world-series-titles (meta giants)) __)
@(:world-series-titles (meta giants))))
"You can also create a new object from another object with metadata"
(= {:league "National League" :park "AT&T Park"}
(meta (vary-meta giants
assoc __ __)))
"But it won't affect behavior like equality"
(= __ (vary-meta giants dissoc :league))
"Or the object's printed representation"
(= __ (pr-str (vary-meta giants dissoc :league))))