Getting the name of a Clojure struct type?

Question

When defining a struct type and instance, I can print the value and get the "struct" implementation type:

(defstruct person :name :age)
(def p (struct person "peter" 30))

user=> p
{:name "peter", :age 30}
user=> (type p)
clojure.lang.PersistentStructMap

But is it possible to tell whether p is an instance of the struct type "person"?

Answer 1

See: http://groups.google.com/group/clojure/browse_thread/thread/a5e0ba6480d04829/3fbd539b807a506d?q=struct+type+group:clojure#3fbd539b807a506d

In general the group archives are a treasure chest...

Note: The functionality of structs is replaces by records. There this is not a problem anymore, because records really define new type and you can check with instance? whether something is of record of a certain type.

Answer 2

A bit ugly, but it works:

(require '[clojure.contrib.java-utils :as cj])

(defn struct-instance? [struct-def sm]
  (= (cj/wall-hack-field clojure.lang.PersistentStructMap "def" sm)
     struct-def))

(struct-instance? person p)
; => true

(struct-instance? person (conj p [:foo 1] [:bar 2]))
; => true

(defstruct foo :k1 :k2)
(struct-instance? foo p)
; => false

Stuff from clojure.contrib.java-utils will be available in 1.2 in part in clojure.java, in part in clojure.contrib.java (I guess?), and also in clojure.contrib.java-utils for backward compatibility... Although the details might still change. At any rate, Meikel is right about defrecord replacing defstruct, so if you're working on 1.2, prefer that.