I have a protocol RestSerializable to represent data that can be serialized
to json from a REST interface.
(defprotocol RestSerializable
(rest-serialize [this]
"Convert to something Cheshire can JSONify"))
By default, things are left alone
(extend Object
RestSerializable
{:rest-serialize identity})
But I want atoms and the like to be transparent when serialized
(extend clojure.lang.IDeref
RestSerializable
{:rest-serialize (comp rest-serialize deref)})
I would expect this to mean that, say,
(-> 42 atom atom atom atom rest-serialize)
would just unwrap to 42, but in fact it only unwraps the outer atom and
leaves the inner ones alone.
Here's where it gets weird though. If I just evaluate the extend
clojure.lang.IDeref form again, rest-serialize suddenly gains the ability
to unwrap *two* layers of atoms. Eval it again and it can unwrap *three*.
Kinda feels like the exercises in Little Schemer when they're building up
to the Y Combinator.
Here's my REPL session demonstrating this (not shown, but I've verified
this behavior is the same in Clojure 1.5.1 and Clojure 1.6.0-alpha3)
$ lein repl
nREPL server started on port 46049 on host 127.0.0.1
REPL-y 0.2.1
Clojure 1.5.1
Docs: (doc function-name-here)
(find-doc "part-of-name-here")
Source: (source function-name-here)
Javadoc: (javadoc java-object-or-class-here)
Exit: Control+D or (exit) or (quit)
Results: Stored in vars *1, *2, *3, an exception in *e
user=> (defprotocol RestSerializable
#_=> (rest-serialize [this]
#_=> "Convert to something Cheshire can JSONify"))
RestSerializable
user=>
user=> (extend Object
#_=> RestSerializable
#_=> {:rest-serialize identity})
nil
user=>
user=> (extend clojure.lang.IDeref
#_=> RestSerializable
#_=> {:rest-serialize (comp rest-serialize deref)})
nil
user=> (-> 7 atom atom atom rest-serialize)
#<Atom@56153406: #<Atom@a0aa211: 7>>
user=> (-> 7 atom atom atom rest-serialize)
#<Atom@3c19a5b0: #<Atom@37cce4a3: 7>>
user=> (-> 7 atom atom atom rest-serialize)
#<Atom@9f6e629: #<Atom@308092db: 7>>
user=> (extend clojure.lang.IDeref
#_=> RestSerializable
#_=> {:rest-serialize (comp rest-serialize deref)})
nil
user=> (-> 7 atom atom atom rest-serialize)
#<Atom@7fb48906: 7>
user=> (-> 7 atom atom atom rest-serialize)
#<Atom@41e224a5: 7>
user=> (extend clojure.lang.IDeref
#_=> RestSerializable
#_=> {:rest-serialize (comp rest-serialize deref)})
nil
user=> (-> 7 atom atom atom rest-serialize)
7
user=> (quit)
Bye for now!
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