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

[Theam Yong Chew]

On 7/17/12, Mark Evenson <evenson at panix.com> wrote:
>
> 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.
>

Thanks Mark & Rudi, good thoughts. I have used my own specific
wrappers in the class, but am looking for something lazier this
time. jcoerce could be what I need for that, while writing a specific
wrapper (as Rudi suggested) could be used in more "formal" settings.

Cheers & happy consing,

Yong