为什么我不能使用Clojure的：^ const与Java字节数组？ [英] Why can't I use Clojure's :^const with a Java byte array?

问题描述

使用Clojure 1.4.0中的 lein repl ，我可以定义一个Java字节数组的 ^：const ，但我不能对它做任何事情：

Using lein repl with Clojure 1.4.0, I can define a ^:const of a Java byte array, but I can't then do anything with it:

user=> (def x (byte-array (map byte [0 1 2 3])))
#'user/x
user=> (alength x)
4
user=> (type x)
[B
user=> (def ^:const cx (byte-array (map byte [0 1 2 3])))
#'user/cx
user=> (alength cx)
CompilerException java.lang.RuntimeException: Can't embed object in code, maybe print-dup not defined: [B@10e6cbd, compiling:(NO_SOURCE_PATH:1)
user=> (type cx)
CompilerException java.lang.RuntimeException: Can't embed object in code, maybe print-dup not defined: [B@10e6cbd, compiling:(NO_SOURCE_PATH:1) 

我已经确认这发生在我的应用程序，所以它不只是一个REPL问题。

I've confirmed this happens in my app as well, so it's not just a REPL issue.

我缺少什么？

推荐答案

^：const形式在编译时被评估，但是在clojure中，编译时值必须是可打印和可读的（由clojure读取器）*。像大多数java对象一样，字节数组是不可打印的或可读的，所以你不能在它们之间创建一个常量。

^:const forms are evaluated at compile time, but in clojure, compile-time values have to be printable and readable (by the clojure reader)*. Like most java objects, byte-arrays aren't printable or readable, so you can't make a constant out of them.

另外，根据文档， ：const只对原语有用。不是原始数组。

Also, according to the docs, ^:const is only useful for primitives. not primitive arrays.

• 另请参见 http://www.infoq.com/presentations/Clojure-Macros 了解相关问题。

• See also http://www.infoq.com/presentations/Clojure-Macros for some related issues.

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