Not getting integer overflow in Clojure?

Question

I am running Clojure 1.3.0 with La Clojure in IntelliJ IDEA while reading The Joy Of Clojure, and on section 4.1.3 (page 64), the authors demonstrate integer overflow with the following code:

(+ Integer/MAX_VALUE Integer/MAX_VALUE)
;=> java.lang.ArithmeticException: integer overflow

However, when I try it out on the REPL, I get instead

user=> (+ Integer/MAX_VALUE Integer/MAX_VALUE)
4294967294

user=> Integer/MAX_VALUE
2147483647

What is happening here? Why are my integers being added correctly instead of overflowing?

@KugathasanAbimaran I copy-pasted all that, so I am pretty sure... :O — wrongusername
– wrongusername, Commented Dec 29, 2011 at 6:03
@wrongusernaem : I'm using 1.2.0 and get that exception. Seems like book [that edition] uses 1.2.0. And gertalot have the solution. — Abimaran Kugathasan
– Abimaran Kugathasan, Commented Dec 29, 2011 at 6:19

Gert · Accepted Answer · 2011-12-29 06:32:03Z

8

(edited) Clojure (at least 1.3.0) automatically converts the integer to a long if necessary. For more details about automatic boxing, promotion and primitive numeric type support in Clojure 1.3.0 check the Documentation for Clojure 1.3.0 Numerics.

The reason you don't get an overflow is because Clojure automatically converts the integer to a long, so (+ Integer/MAX_VALUE Integer/MAX_VALUE) is adding two longs:

user> (type Integer/MAX_VALUE)
java.lang.Long

edited Dec 29, 2011 at 6:32

answered Dec 29, 2011 at 5:51

Gert

3,85921 silver badges22 bronze badges

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

Comments

Arthur Ulfeldt · Accepted Answer · 2011-12-30 02:27:45Z

8

In Clojure all primative integers are primative longs and the documentation on the numerics page is refering to that. in 1.3 you just need bigger numbers to get your overflow.

user=> (+ Long/MAX_VALUE Long/MAX_VALUE)
ArithmeticException integer overflow  clojure.lang.Numbers.throwIntOverflow (Numbers.java:1374)

This important part is that older versions of clojure would have promoted to a big int automatically and it was decided that the cost of this was not worth the extremely rare cases where it is desired. if you really want promoting math use +'

user=> (+' Long/MAX_VALUE Long/MAX_VALUE)
18446744073709551614N

answered Dec 30, 2011 at 2:27

Arthur Ulfeldt

91.7k30 gold badges205 silver badges285 bronze badges

Collectives™ on Stack Overflow

Not getting integer overflow in Clojure?

2 Answers 2

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related