[armedbear-devel] Longs, Bytes, or casting in general

[Mark Evenson]

On Jul 17, 2012, at 04:19 , Theam Yong Chew wrote:

> Hi folks,
> 
> I was wondering how we can conveniently pass longs, bytes into normal
> Java functions/constructors, for example,
> 
> (jnew "java.lang.Byte" 23)
> ==>
> Java exception 'java.lang.NoSuchMethodException: Byte(java.lang.Integer)'.
>   [Condition of type JAVA-EXCEPTION]
> 
> Here only constructor available is for "byte" inputs. It's a pain to
> have to use this every time we use a byte, long, or similar:
> 
> (jnew (jconstructor "java.lang.Byte" "byte") 23)
> #<java.lang.Byte 23 {3A9300BF}>

Unfortunately, I can't think of a way around this off the top of
my head, although I may be missing something.  I suppose what we
would want would be some sort of algorithm that would keep trying
constructors by casting the types of parameters up/down their
inheritance trees until it found a match.  Although it would be
rather unsafe (from thinking about it briefly about casting things
between signed/unsigned representation), it might be useful enough
to construct something for experimentation.

> Relatedly/alternatively, is there a way convenient to coerce values to
> a certain type, forcing 23 above (default int/Integer) to be a byte or
> long?

JCOERCE does this:

   CL-USER> (jcoerce 23 "byte")
   #<java.lang.Byte 23 {3A5F299D}>

although it always wraps primitive types in the associated numeric tower class.