What is the Clojure equivalent of a “public static final” constant in Java

Question

I'm writing some Clojure code that depends upon a number of constants.

They will be used within tight inner loops, so it's important that they will be used and optimised as efficiently as possible by the Clojure compiler+JVM combination. I would normally used a "public static final" constant in Java for the same purpose.

What is the best way to declare these?

Answer 1

我认为def全局命名空间-ing的事情是最接近你能来。

Answer 2

I believe Clojure 1.3 (or maybe 1.4) allows you to put a ^:constant tag on a def , signifying to the compiler that this should be a constant and all references should be resolved at compile-time.

Edit

Apparently it's Clojure 1.3, and it's ^:const , not ^:constant . See How does Clojure ^:const work? for a summary.

Answer 3

There's no defconst , so just using a global def is idiomatic; as far as optimisation is concerned, the JIT will make things fast.

Answer 4

If really, really, really want the constant in place (I believe, the JIT will notice the value being constant and do the right thing, though), you can use a macro.

(defmacro my-constant [] 5)

This is rather ugly, but performance critical code will always be ugly, I guess.

(do-stuff (my-constant) in-place)

Pay care what you put into the macro, though! I wouldn't this for more than some literal constants. In particular not objects.

Answer 5

如果只使用def不够快，你可以尝试在进入紧密循环之前创建一个let绑定别名，以避免每次都通过var。

Answer 6

如上所述使用def或atom，记住，数据是不可变的，所以如果你在列表中声明一些常量，它们就不会改变。