Using a protocol with primitive arguments

Question

I'm trying to define a protocol in Clojure 1.4 with primitive arguments (so that I can avoid unnecessary primitive boxing in performance-sensitive code):

(defprotocol A
  (foo [a ^long x]))

(extend-type java.lang.String A 
  (foo [s ^long x] (.charAt s x)))

This look like it works OK but fails with an exception when I try to use it:

(foo "abracadarbra" 3)
=> ClassCastException XXXX cannot be cast to clojure.lang.IFn$OLO

What am I doing wrong?

mikera · Accepted Answer · 2012-08-28 05:59:16Z

3

After some further reasearch it appears that protocols do not yet support primitive type hints (as of Clojure 1.4). See e.g. https://groups.google.com/d/topic/clojure-dev/HxBqIewc494/discussion

Alternatives seem to be:

Write regular functions with primitive hints. You lose polymorphism.
Use a Java interface (you can use reify to build instances in Clojure)

answered Aug 28, 2012 at 5:59

mikera

107k28 gold badges265 silver badges427 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Arthur Ulfeldt · Accepted Answer · 2012-08-28 05:10:16Z

2

take the type hint out of the defprotocol and leave it in the extend-type

(defprotocol A
(foo [a x]))

(extend-type java.lang.String A 
  (foo [s ^Long x] (.charAt s x)))
nil
core> (foo "abracadarbra" 3)
\a

or you can change the type hint like so:

(defprotocol A
(foo [a ^Long/TYPE x]))

(extend-type java.lang.String A 
  (foo [s ^long x] (.charAt s x)))
nil
core> (foo "abracadarbra" 3)
\a

this still produces no reflection warnings without the hint in the defprotocol

EDIT:

(extend-type java.lang.String A 
  (foo [s ^Long x] (type x)))
nil
core> (foo "abracadarbra" 3)
java.lang.Long

edited Aug 28, 2012 at 5:10

answered Aug 28, 2012 at 4:28

Arthur Ulfeldt

91.7k30 gold badges205 silver badges285 bronze badges

3 Comments

mikera Over a year ago

thanks Arthur! this works - but is it actually using the primitive version of the function?

mikera Over a year ago

Hmmm not quite solving the problem then as my intention was to find a way to avoid boxing of primitive arguments.....

Arthur Ulfeldt Over a year ago

I may be reading that wrong, it's hard to tell because (type 4) reports the same...

Collectives™ on Stack Overflow

Using a protocol with primitive arguments

2 Answers 2

Comments

3 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

3 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related