[Armedbear-devel] Comments on Cyrus's proposal for JSS static calls

[Alan Ruttenberg]

On Thu, Aug 21, 2014 at 3:17 PM, Cyrus Harmon <ch-lisp at bobobeach.com> wrote:

>
> On Aug 20, 2014, at 11:14 PM, Mark Evenson <evenson at panix.com> wrote:
>
> Erik asked me to comment on [Cyrus’s proposed patch][1] to extend JSS’s
> SHARPSIGN-DOUBLE-QUOTE use in static method calls to accept a string as
> well as
> a symbol to designate the object.
>
>
> Thanks for taking a look.
>
>
> Unfortunately, changing JSS in the manner means that one can no longer use
> SHARPSIGN-DOUBE-QUOTE on object descended from java.lang.String, for the
> reasons described in the [JSS README][2]:
>
> […]
> Static calls are possible as well with the #" macro, but the
> first argument MUST BE A SYMBOL to distinguish
>
>     (#"getProperties" "java.lang.System")
>
> from
>
>     (#"getProperties" 'java.lang.System)
>
> How about
   (#2"getProperties" "java.lang.System")

We could make that work. (or any number other than 0 or 1 - I thought 8
might be nice since if you squint through a vertical bandpass it would look
like two pairs of quotes stacked ;).


> The first attempts to call a method on the java.lang.String object
> with the contents "java.lang.System", which results in an error, while
> the second invokes the static java.lang.System.getProperties() method.
> […]
>
>
> It wasn’t (isn’t) at all clear to me that in the first example we’re
> trying to call a method on a java.lang.String object. In fact I thought
> lisp strings and java strings were distinct classes (not exactly in the
> CLOS or java sense) of objects:
>
> *ABCL-CDK> "foo"*
> *"foo"*
>
> *ABCL-CDK> (java:jnew "java.lang.String" "foo")*
> *#<java.lang.String foo {64E135F}>*
>
> I would have thought that calling a method on a string would have failed.
> But, of course, I am wrong:
>
> *ABCL-CDK> (#"getBytes" (java:jnew "java.lang.String" "foo"))*
> *#<jarray [B at 57027b0d {63DCBF1B}>*
>
> *ABCL-CDK> (#"getBytes" "foo")*
> *#<jarray [B at 3d0c15a {7E45FDAA}>*
>
> So, somewhere along the line “foo” is being treated as a java.lang.String.
> Hmm… Now I see your objection to my patch.
>
> Other than perhaps for aesthetic reasons, is there some functionality that
> using strings enables here?  To argue about preserving character case in
> strings as opposed to the case folding implicit in symbols doesn’t seem to
> be
> applicable, because JSS currently ignores case when searching for matching
> JVM
> symbols.  In 2006, when I first understood the ignoring case bit of JSS, I
> was
> a bit worried that there would be cases where this resulted in ambiguity
> and
> errors, but in the ensuing years I have yet to run into a single problem
> with
> this design decision.
>
>
> I don’t like using naked strings as class identifiers as they’re too long
> to type and too error prone. So I use variables that evaluate to strings:
>
>
> *(defmacro jimport (java-package class &optional package)*
> *  `(eval-when (:compile-toplevel :load-toplevel :execute)*
> *    (defparameter ,(apply #'intern class*
> *                          (when package (list package)))*
> *      (concatenate 'string (symbol-name (quote ,java-package))*
> *                   "."*
> *                   (symbol-name (quote ,class))))))*
>
> *(jimport |java.util| |Vector|)*
>
> This lets me do:
>
> *(java:jnew |Vector|)*
>
> and, with my patch,
>
> *ABCL-CDK> (jimport |java.lang| |System|)*
> *|System|*
> *ABCL-CDK> (#"getProperties" |System|)*
> … which fails on a stock ABCL.
>
> A minor convenience, I’ll admit.
>
> Therefore, I am not currently persuaded that introducing an asymmetry to
> SHARPSIGN-DOUBLE-QUOTE (“It works on any java Object except those which
> descend
> from java.lang.String; for those instances you have to use the JFI”) to use
> strings as well as symbols to specify static methods is worth it.  But
> please
> argue back if you disagree…
>
>
> I was trying to make it work on any object that isn’t a lisp string, not
> realizing that lisp and java strings are more closely related than I
> thought.
>
> thanks for the feedback,
>


> Cyrus
>
>
> [1]:
> https://github.com/slyrus/abcl/commit/9ec0fb26c7b7e9470349b1c4bd9be6fa4b053177
> [2]:
> http://abcl.org/trac/browser/trunk/abcl/contrib/jss/README.markdown#L55
>
> --
> "A screaming comes across the sky.  It has happened before but there is
> nothing
> to compare to it now."
>
>
>
>
>
>
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