From: Glen Starchman <glen@...>
Date: 2001-05-17T02:08:01+09:00
Subject: [ruby-talk:15301] Re: Ruby in Java

> I'm not familiar with Jython, but providing a BSF compatible interpreter 
> would have certain benefits; primarily, that many existing applications could 
> automatically plug the Ruby interpreter into themselves.

Jython allows you to write code that looks exactly like Python. For
example:

class test:
    def __init__(self):
        print "initializing!"

    def test_func(self, x):
        print x

which would (roughly) translate to the following Java:

import java.lang.*;
import PyCore.*;
/* import a bunch of Jython support classes here... */
public class test
{
    test()
    {
         PyString s1 = new PyString("initializing!");
        System.out.println(s1);
    }

    public void test_func(PyObject x)
    {
        System.out.println(x);
    }
}

where PyString and PyObject have a toString() method that allows them
to work with println. 

You can see that in a large project you end up with lots of code like
PyString py=new PyString(...) and the like. Pretty ugly stuff...

      

> 
> > 1) a Ruby interpreter, and all supporting libraries, ported to Java
> > 2) A Ruby-Java "translator" that makes use of the above libraries and
> > interfaces seamlessly with Java.
> 
> Is (2) a Ruby-to-Java translator?  And, by (1), I'm assuming you mean that 
> you could do all of the following:

> 
> 1)	String result = ruby.Ruby.eval( " %w{a b c d e f}.find{|n| n == 'c'} " );
> 	// => "c"

Sure. You should have access to the Ruby eval-print loop.

> 2)	$ java -cp ruby.jar irb.rb
> 	irb(main):001:0> p "Hello World"
> 	"Hello World"
> 	nil

In jython the paradigm is:
$jython
Jython 2.1a1 on java1.3.0_02 (JIT: null) ...

One thing that Jython does do very well is package up all of the
necessary code into a nice little jar files... with the -c and -d
options, it also takes care of bundling up all of the necessary Jython
support files. So, after compiliation and bundling, you get a true Java
jar that is not dependent on the end user having Jython (or
Python) installed:

$java -jar JythonApp.jar


> 	irb(main):002:0>
> 3)	String result = (new ruby.Regex("/(.)(.)(.)/")).match("abc")[2];
> 	System.out.println( result ); // => "b"


I think the code would end up looking something like:

import ruby;
...

ruby.Regex regex = new ruby.Regex(/(.)(.)(.)/"));
List results = (List)regex.match("abc");
String result = results.elementAt(2);

(or somethink like that!) from "pure" Ruby code. 


> I'm sure the last would be useful, although you'd lose most of the Ruby good 
> stuff.

You don't necessarily have to, I don't think... although things like
code blocks would be a very trying thing to implement in Java... ;-)