Mirah Office Hours: try again at class loading

So last week I got hung up on the classloader bug. This week I tried to find a workaround for it. It didn’t work but I learned a lot. Did too work!


  • Bug Triage
  • fix easy bugs
  • class loader workaround
  • after parse callback
  • argv
  • ….
  • $$$$

I started with doing some bug triage. I looked at issues starting from the oldest in github issues, and tried to resolve them. I closed #26, #99, #119, #114. Some of them were already fixed, others were covered by other issues and some I fixed myself.

I also commented on a few issues asking for clarification.

#26 I couldn’t reproduce any more

#99 Isn’t exactly a bug, though it’d be nice if []= could be defined as a method without a macro.

#114 was a problem where a type error wasn’t being handled properly when a method was passed a block. The initial error caused the arguments lookup for the block to fail, blowing up.

#119 the problem here was that the method to transform an empty array literal wasn’t implemented. I cribbed the behavior of transform_zsuper to come up with something that worked.

After the bugs, I looked at

a class loader workaround

I thought, if the problem is that a class loader written in JRuby wouldn’t work, maybe one written in Mirah would. Unfortunately, I couldn’t get it working.

Converting the old code was surprisingly easy to do, which was nice. (gist’s below)


became this:

But then I ran into a snag.

The problem was that the string containing the bytecode being passed around was getting converted to UTF-8. Which did not make Java very happy.

Java expects all it’s .class files to start with the value 0xCAFEBABE. Instead, the strings the class loader got began with 0xEFBFBDEF, which it didn’t like at all.

So, I went on a search for the right encoding. I tried passing UTF-8, UTF-16 BE and LE–the lot of the charsets on the Charset Javadoc–to getBytes in the ClassLoader. That didn’t work.

I tried changing the Map I was passing to the ClassLoader from classname -> String ‘o bytes to classname -> byte[]. That almost worked, but I couldn’t cast the byte array on the Mirah side.

Then I looked up binary encodings and Java and found this interesting gem. Turns out I’m not the only one whose run into this encoding issue. I followed the suggested workaround using the ISO-8859-1 charset. And it worked! Huzzah!

Comments are closed.