mwilliamson/java-couscous

Convert Java source code to other languages. C# and Python currently supported.

Couscous

Convert Java source code to other languages. C# and Python currently supported.

Hello world: Java to C#

1. Build the JAR:

   mvn package -Dmaven.test.skip=true
   

2. Create a Java source file:

   package com.example;
   
   public class Example {
       public static void main() {
           System.out.println("Hello world");
       }
   }

   Assuming the normal Maven layout, this file should be at src/main/java/com/example/Example.java.

3. Create a file called couscous.json:

   {
     "backend": "csharp",
     "sourcepath": [
       "src/main/java"
     ],
     "files": [
       "src/main/java/com/example",
     ],
     "output": "dotnet/generated.cs",
     "namespace": "Example"
   }
   

4. In the directory containing couscous.json:

   java -jar path/to/couscous.jar
   

   This should generate the file dotnet/generated.cs, which looks something like:

   namespace Example.com.example {
       internal class Example {
           public static void main() {
               (Example.java.lang.System._out).println("Hello world");
           }
       }
   }

   Couscous provides very little runtime support: in this case, an implementation of System.out.println(String) will need to be written.

TODO

• Put for-loops and similar into their own block. Otherwise, for instance, two for-loops in the same scope using the same name for their loop variable will cause a variable re-definition in C#.

• Multiple constructors

• Remove all direct runtime support

• Type names for generics

• Type erasure

• Boxing and unboxing for Strings

• Handle boxing/unboxing when overriding method in supertype with more/less specific return types/arguments. For instance, if an interface defines a method that returns Object, then a subtype may override that method returning Integer. We want Integer to be unboxed (in general), so that calling the method on the subtype returns an unboxed Integer, but if the caller is calling the method on the supertype, it will expect an Object, meaning it will need to be boxed. This probably means having two overloads -- one for the supertype, one for the subtype.

  This needs doing regardless of changes to boxing/unboxing primitives since we currently use raw strings rather than boxing them into Java strings.

Python precedence

The table below gives precedence from lowest to highest in Python 3.5. Some rows have the same precedence for serialisation to improve code clarity.

Operator	Precedence (serialisation)
lambda	0
if – else	10
or	20
and	20
not x	40
in, not in, is, is not, <, <=, >, >=, !=, ==	50
`	`
^	70
&	80
<<, >>	90
+, -	100
*, @, /, //, %	110
+x, -x, ~x	120
**	130
await x	140
x[index], x[index:index], x(arguments...), x.attribute	150
(expressions...), [expressions...], {key: value...}, `{expressions...}``	160