Re: [Jython-users] Jython documentation

[Alexander S. <ast...@ma...>]

On Jan 20, 2007, at 5:25 AM, Diez B. Roggisch wrote:

>> 2) Jython (non)interaction with java generics
>> Jython completely ignores java generics. In my opinion this is   
>> trivial but non-obvious. It is trivial once I remember that java   
>> generics have no support in the JVM and are essentially compile  
>> time  magic (please correct me if i am wrong on this).  It is non- 
>> obvious  because I don't normally think about such things when  
>> just using  code. I wouldn't have seen this behavior without  
>> deliberately setting  out to test it.
>> Generics provide no type safety to jython scripting on java   
>> collections. I suspect this could be the source of nasty bugs for  
>> the  unwary. Is this issue worthy of documenting?
>
> Why do you single out generics? There is no type annotation support  
> in jython _anywhere_, it is the very reason I prefer jython over  
> java in most cases.
>
> So why should anybody expect
>
> foo = "bar"
> foo = 100
>
> to work, while
>
> map.put("foo", 100)
> map.put(100, "foo")
>
> expect to puke with type errors?

I was thinking specifically of the case of interacting with existing  
java libraries. Java methods still demand correct typing when used  
from jython. You get errors when doing things like:
 >>> d = java.util.Date("'100")

And the same would be true for methods on any java classes one has  
written. However misusing a java generic will give no such error. So  
you may get a deferred type error in java code which a java  
programmer would think has been prevented by specifying the generic.

So the issue isn't  the lack of type safety in jython, which I agree  
is generally a gain, but the "odd" behavior of generic typing in java  
code called from jython. Without thinking carefully about it one  
might start looking for bugs in the wrong places.

Alex