Hi all,
after digging around a bit in the clojure code, trying to get the
compile to work, I found out that classes used by the compiled code
actually classloaded by the compiler.
I can totally get behind the idea that code is data. But in this case
data is considered code, and is immediately executed. This leads to
all kinds of fun.
fun.clj:
(defn foo [] (new mostly.Harmless))
mostly/Harmless.java:
package mostly;
public class Harmless {
static {
System.exit(42);
}
}
Try compiling these two files. The clojure compiler just silently
exits. I admit the example is a bit extreme and needlessly malicious,
but there are valid uses for class initializers. I guess clojure files
might suffer from the same problems.
I sort of understand that for clojure compile time is runtime, but I
still find it quite odd that a language that puts so much emphasis on
avoiding side-effects would allow code to be executed as a side-effect
of compilation. Shouldn't compilation be a theoretically pure function
transforming a set of source files into a set of class files?
I guess one way to achieve this would be to use "Class handles",
instead of raw Class objects. Depending on situation these class
handles could either delegate to Class instances or use asm to get the
required information. This might be a best of both worlds solution.
Especially for IDE's and build tools like ant or maven these
compilation side effects can wreak havoc to the surrounding execution
context.
Cheers
- Manuel Woelker
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