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added basic example of protocol paths to README

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Nathan Marz 2015-12-13 13:38:16 -05:00
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README.md
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@ -145,6 +145,37 @@ user> (transform [ALL (if-path [:a even?] [:c ALL] :d)]
[{:c [2 3], :d 4, :a 2} {:c [1 11 0], :a 4} {:c [1 1 1], :d 2, :a -1}]
```
"Protocol paths" can be used to navigate on polymorphic data. For example, if you have two ways of storing "account" information:
```clojure
(defrecord Account [funds])
(defrecord User [account])
(defrecord Family [accounts-list])
```
You can make an "AccountPath" that dynamically chooses its path based on the type of element it is currently navigated to:
```clojure
(use 'com.rpl.specter.macros)
(defprotocolpath AccountPath [])
(extend-protocolpath AccountPath
User :account
Family [:accounts-list ALL])
```
Then, here is how to select all the funds out of a list of `User` and `Family`:
```clojure
user> (select [ALL AccountPath :funds]
[(->User (->Account 50))
(->User (->Account 51))
(->Family [(->Account 1)
(->Account 2)])
])
[50 51 1 2]
```
You can make `select` and `transform` work much faster by precompiling your selectors using the `comp-paths` function. There's about a 3x speed difference between the following two invocations of transform:
```clojure