Re: easier Kawa object building with Swing example

[Jamison Hope <jrh at theptrgroup dot com>]

On Oct 1, 2010, at 11:47 AM, Per Bothner wrote:

> For a while Kawa has supported:
>  (MyClass keyword1: value1 ... kewordN: valueN)
> as shorthand for:
>  (let ((tmp (make MyClass)))
>    (set! tmp:keyword1 value1)
>    ...
>    (set! tmp:keywordN valueN)
>    tmp)
> where
>  (set! tmp:keywordI valueI)
> could compile to either setting a field or calling a setKeywordI  
> method.

I have a number of setters which have the general form:

public <ObjType> setFoo(<FooType> arg) {
  this.foo = arg;
  return this;
}

It's a style I picked up from Objective-C which has proven handy in  
constructs like
"container.add(new ObjType().setFoo(foo).setBar(bar));"
letting me avoid assigning my new object to a local variable just to  
call some methods on it before handing it off to something else. It's  
roughly the Java equivalent of this Kawa keyword setter style.

Anyway, I have found that Kawa's keyword style fails with my setters:

$ cat test/A.java
> package test;
>
> public class A {
>   private int x;
>   private String y;
>
>   public A setX(int arg) { x = arg; return this; }
>
>   public int getX() { return x; }
>
>   public A setY(String arg) { y = arg; return this; }
>
>   public String getY() { return y; }
>
>   public String toString() { return super.toString() + ",x="+x 
> +",y="+y; }
> }
$ cat test/B.java
> package test;
>
> public class B extends A {
>   private float z;
>
>   public B setZ(float arg) { z = arg; return this; }
>
>   public float getZ() { return z; }
>
>   public String toString() { return super.toString() + ",z="+z; }
> }
$ javac test/A.java test/B.java
$ java kawa.repl
> #|kawa:1|# (define a (test.A))
> #|kawa:2|# (define b (test.B))
> #|kawa:3|# (define a (test.A x: 42))
> exception while initializing module atInteractiveLevel$3
> 	at gnu.expr.ModuleContext.findInstance(ModuleContext.java:84)
> 	at gnu.expr.ModuleExp.evalModule2(ModuleExp.java:274)
> 	at gnu.expr.ModuleExp.evalModule(ModuleExp.java:185)
> 	at kawa.Shell.run(Shell.java:281)
> 	at kawa.Shell.run(Shell.java:194)
> 	at kawa.Shell.run(Shell.java:175)
> 	at kawa.repl.main(repl.java:847)
> Caused by: java.lang.VerifyError: (class: atInteractiveLevel$3,  
> method: run signature: (Lgnu/mapping/CallContext;)V) Incompatible  
> object argument for function call
> 	at java.lang.Class.getDeclaredFields0(Native Method)
> 	at java.lang.Class.privateGetDeclaredFields(Class.java:2291)
> 	at java.lang.Class.getDeclaredField(Class.java:1880)
> 	at gnu.expr.ModuleContext.findInstance(ModuleContext.java:74)
> 	... 6 more
> #|kawa:4|# (test.A x: 42)
> test.A@76497934,x=42,y=null
> #|kawa:5|# (define b (test.B z: 1.5))
> exception while initializing module atInteractiveLevel$5
> 	at gnu.expr.ModuleContext.findInstance(ModuleContext.java:84)
> 	at gnu.expr.ModuleExp.evalModule2(ModuleExp.java:274)
> 	at gnu.expr.ModuleExp.evalModule(ModuleExp.java:185)
> 	at kawa.Shell.run(Shell.java:281)
> 	at kawa.Shell.run(Shell.java:194)
> 	at kawa.Shell.run(Shell.java:175)
> 	at kawa.repl.main(repl.java:847)
> Caused by: java.lang.VerifyError: (class: atInteractiveLevel$5,  
> method: run signature: (Lgnu/mapping/CallContext;)V) Incompatible  
> object argument for function call
> 	at java.lang.Class.getDeclaredFields0(Native Method)
> 	at java.lang.Class.privateGetDeclaredFields(Class.java:2291)
> 	at java.lang.Class.getDeclaredField(Class.java:1880)
> 	at gnu.expr.ModuleContext.findInstance(ModuleContext.java:74)
> 	... 6 more
> #|kawa:6|# (test.B z: 1.5)
> test.B@3d9360e2,x=0,y=null,z=1.5
> #|kawa:7|# (test.B z: 1.5 x: 42)
> test.B@6766afb3,x=42,y=null,z=1.5
> #|kawa:8|# (test.B x: 42 z: 1.5)
> exception while initializing module atInteractiveLevel$8
> 	at gnu.expr.ModuleContext.findInstance(ModuleContext.java:84)
> 	at gnu.expr.ModuleExp.evalModule2(ModuleExp.java:274)
> 	at gnu.expr.ModuleExp.evalModule(ModuleExp.java:185)
> 	at kawa.Shell.run(Shell.java:281)
> 	at kawa.Shell.run(Shell.java:194)
> 	at kawa.Shell.run(Shell.java:175)
> 	at kawa.repl.main(repl.java:847)
> Caused by: java.lang.VerifyError: (class: atInteractiveLevel$8,  
> method: run signature: (Lgnu/mapping/CallContext;)V) Incompatible  
> object argument for function call
> 	at java.lang.Class.getDeclaredFields0(Native Method)
> 	at java.lang.Class.privateGetDeclaredFields(Class.java:2291)
> 	at java.lang.Class.getDeclaredField(Class.java:1880)
> 	at gnu.expr.ModuleContext.findInstance(ModuleContext.java:74)
> 	... 6 more


and so on. I find it especially interesting that in some cases,  
assigning to a variable triggers the Exception
(e.g. "(test.A x: 42)" works, but "(define a (test.A x: 42))" blows up).

If I change setX(), setY(), and setZ() all to return void instead,  
then Kawa works as expected:

$ java kawa.repl
> #|kawa:1|# (define a (test.A))
> #|kawa:2|# (define b (test.B))
> #|kawa:3|# (define a (test.A x: 42))
> #|kawa:4|# (test.A x: 42)
> test.A@76497934,x=42,y=null
> #|kawa:5|# (define b (test.B z: 1.5))
> #|kawa:6|# (test.B z: 1.5)
> test.B@3d9360e2,x=0,y=null,z=1.5
> #|kawa:7|# (test.B z: 1.5 x: 42)
> test.B@6766afb3,x=42,y=null,z=1.5
> #|kawa:8|# (test.B x: 42 z: 1.5)
> test.B@5975d6ab,x=42,y=null,z=1.5

But then I lose functionality on the Java side, so that's not really  
desirable. Any ideas why non-void-return setters would break
 (let ((tmp (make MyClass)))
   (set! tmp:keyword1 value1)
   ...
   (set! tmp:keywordN valueN)
   tmp)
?

Thanks,
Jamie

Oh, by the way, Kawa is being noisy about unboxing booleans:
$ java kawa.repl
> #|kawa:1|# (javax.swing.JPanel visible: #f)
> /dev/stdin:1:1: warning - type java.lang.Boolean is incompatible  
> with required type boolean
> javax.swing.JPanel[, 
> 0,0,0x0 
> ,invalid 
> ,hidden 
> ,layout 
> = 
> java 
> .awt 
> .FlowLayout 
> ,alignmentX 
> = 
> 0.0 
> ,alignmentY 
> =0.0,border=,flags=9,maximumSize=,minimumSize=,preferredSize=]


That's probably analogous to the conversions between integer and the  
numeric primitives I brought up last week.

--
Jamison Hope
The PTR Group
www.theptrgroup.com