Clojure - why can I call (Integer/MAX_VALUE) as a function?

Question

An example probably explains it best. Why does the 2nd and 3rd examples work?

Integer/MAX_VALUE
=> 2147483647
(Integer/MAX_VALUE)
=> 2147483647
((((((Integer/MAX_VALUE)))))) ; wtf?
=> 2147483647

(1) ; crashes as expected
Execution error (ClassCastException) at medino-web.handler/eval7997 (form-init17779606850549883231.clj:1).
class java.lang.Long cannot be cast to class clojure.lang.IFn (java.lang.Long is in module java.base of loader 'bootstrap'; clojure.lang.IFn is in unnamed module of loader 'app')

Eugene Pakhomov · Accepted Answer · 2025-01-27 18:01:53Z

6

From the source code of Clojure 1.12:

// Preserving the existing static field bug that replaces a reference in parens with
// the field itself rather than trying to invoke the value in the field. This is
// an exception to the uniform Class/member qualification per CLJ-2806 ticket.
if(fexpr instanceof StaticFieldExpr)
    return fexpr;

So it seems that that behavior is a bug that was deliberately not fixed to avoid breakage to any existing code that might be relying on it.

answered Jan 27 at 18:01

Eugene Pakhomov

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2 Comments

amalloy Jan 27 at 22:10

I feel like in ye olde days, like back in 2010, it used to be pretty normal to write (Integer/MAX_VALUE). It's certainly been allowed since at least 1.0, so I think it's a bit silly for the author(s) to call it a "bug" when it's been left unfixed for 15 years, and never will be fixed because of backwards compatibility.

Eugene Pakhomov Jan 27 at 22:13

I don't think it's silly - it discourages using that syntax. And prior to CLJ-2806 it wasn't important at all, so I assume that's why it wasn't really labeled as a bug before. Similar to how clojure.set functions returning reasonable results for some combinations of non-set arguments is not labeled as a bug.

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