Forgive me for resurrecting a 7 year old thread, but is this still the
solution?
On Thursday, June 26, 2008 at 7:56:18 AM UTC-7, Chas Emerick wrote:
>
> At some point, I came to need to define a generated Java class that
> had methods that returned instances of the class being generated. The
> gen-and-save-class form looked like this:
>
> (gen-load-save-class
> "."
> 'pkg.Foo
> :implements [Bar]
> :init 'new-foo
> :constructors {[(. Float TYPE)] []}
> :methods [['union [java.util.Collection] 'pkg.Foo]] ;<---
> :state 'state)
>
> The problem is with the usage of 'pkg.Foo in the union method
> signature def. gen-class expects classes for those signature
> definitions, and since the pkg.Foo class doesn't exist yet, I can't
> reference it in the signature.
>
> On a lark, I thought I'd try a macro that would generate and load a
> class (without any references to the generated class), and then
> generate and save that same class with all of the method definitions,
> etc. (By no means efficient, since the bytecode is being generated
> twice, but this is mostly fun and I didn't want to futz with using gen-
> class directly and then handling writing out or loading the bytecode.)
> The result is this:
>
> (defmacro gen-load-save-class [path name & options]
> (let [optmap (apply hash-map options)
> save-only-opts #{:methods :constructors}
> trimmed-opts (reduce #(if (save-only-opts %2) %1 (concat %1
> [%2] [(optmap %2)])) [] (keys optmap))]
> `(do (gen-and-load-class ~name ~@trimmed-opts)
> (eval '(gen-and-save-class ~path ~name ~@options)))))
>
> gen-load-save-class has the same signature as gen-and-save-class. It
> pulls out the options to gen-class that can contain self-references
> (only :methods and :constructors at the moment, I believe), generates
> and loads the result of that trimmed-down option set, and then
> generates and saves the full class definition.
>
> One interesting wrinkle is that the gen-and-save-class form needs to
> be wrapped in an eval; otherwise clojure will attempt to resolve
> references to the generated classname in the options to gen-and-save-
> class before it even gets to the point of evaluating the gen-and-load-
> class call.
>
> I know Rich is aware of this use-case (referring to the generated
> classname when using gen-class), so a real solution will probably be
> forthcoming sooner or later, but this was an interesting exercise in
> the meantime.
>
> - Chas
>
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