[armedbear-devel] MAKE-IMMEDIATE-OBJECT and JOBJECT-LISP-VALUE conceptual problem
alanruttenberg at gmail.com
Sat Jun 11 07:06:35 UTC 2011
I've always disliked make-immediate-object. Really it serves the
purpose of disambiguating a few overloaded values in lisp. I'd like to
deprecate it in favor of specific constants for java-true, java-false
and null-pointer (the latter is already available as function).
It seems dangerous to assume that one can get some java array as the
underlying object below a lisp array, what with all the hair that lisp
arrays can have. Better to allocate your buffer with (jnew-array
"byte" 8192) and not get into this game. Or have a documented policy
of how java objects correspond to lisp objects and promise to support
On Fri, Jun 10, 2011 at 11:42 AM, Mark Evenson <evenson at panix.com> wrote:
> Today, I spent a bit of time trying to figure out a way to efficiently
> compute message digest for Quicklisp. After confirming that
> java.security.MessageDigest implements the required digests, I noticed we
> didn't have a way to easily get at the underlying Java byte array in
> (SIMPLE-VECTOR (UNSIGNED-BYTE 8)). So, I patched the underlying Java code
> as attached, and wrote the following routine:
> (defun sha-256 (path)
> (let ((buffer (make-array 8192 :element-type '(unsigned-byte 8))
> (digest (jstatic "getInstance" "java.security.MessageDigest"
> (with-open-file (in path :element-type '(unsigned-byte 8))
> (loop :for bytes = (read-sequence buffer in)
> :while (plusp bytes)
> :do (jcall-raw "update" digest (make-immediate-object buffer) 0
> (jcall "digest" digest)))))
> But then I noticed that MAKE-IMMEDIATE-OBJECT calls JOBJECT-LISP-VALUE which
> makes no conceptual sense. The doc for MAKE-IMMEDIATE-OBJECT reads
> "[a]ttempts to coerce a given Lisp object into a java-object" while the doc
> JOBJECT-LISP-VALUE reads "Attempts to coerce JAVA-OBJECT into a Lisp
> object". This seems wrong here, but I don't understand how exactly. I
> think we need to distinguish three types of values here: JAVA-OBJECT,
> LispObject, and the "raw" value of the Java. How should we really structure
> our Java FFI here?
> With my patch, for an underlying lisp value of type (SIMPLE-VECTOR
> (UNSIGNED-BYTE 8)), both MAKE-IMMEDIATE-OBJECT and JOBJECT-LISP-OBJECT
> return the byte array. I would think that MAKE-IMMEDIATE-OBJECT should
> just do this, which JOBJECT-LISP-OBJECT should .... return an error if its
> argument isn't of type JAVA-OBJECT? I don't know. I am confused.
> Can someone help me understand the right way forward here?
> "A screaming comes across the sky. It has happened before, but there
> is nothing to compare to it now."
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