How do I check if a value is a promise?

Question

How do I check if a value is a promise?

Availability:

(def x (promise))

How can I check if type x is a promise?

thank

+3

clojure

reshefm 04 Feb At 15:37

source to share

2 answers

I would go with

(defn promise? [p]
  (isa? (class p) clojure.lang.IPending))

+2

skuro 04 Feb At 15:44

source to share

Nikita Beloglazov · Accepted Answer · 2013-02-04T15:45:01+0000

I would say that you cannot at all. Since both parties are created as reify

several interfaces: IDeref

, IBlockingDeref

, IPending

, IFn

. But you can check whether the value of one of them implements: clojure.lang.IPending

.

(defn promise? [v]
  (instance? clojure.lang.IPending p))

Or maybe even everything:

(defn promise? [v]
  (every? #(instance? % v) 
         [clojure.lang.IPending 
          clojure.lang.IFn 
          clojure.lang.IBlockingDeref 
          clojure.lang.IDeref]))

How do I check if a value is a promise?

More articles: