Weak references do work, and it looks like I can just stuff values into a
single java.util.WeakHashMap under gensym-generated keys and not worry
about polluting namespaces. Still kind of hacky, but seems to work.
On Wed, Aug 28, 2013 at 10:28 AM, Jamie Brandon <
ja...@scattered-thoughts.net> wrote:
> You will also run into problems if your functions close over any data:
>
> user> (let [f (fn [] 1)] (eval `(~f)))
> 1
> nil
> user> (let [x 1 f (fn [] x)] (eval `(~f)))
> IllegalArgumentException No matching ctor found for class
> user$eval38616$f__38617 clojure.lang.Reflector.invokeConstructor
> (Reflector.java:163)
>
> I'm struggling with this as well, I'm definitely interested in finding
> a non-hacky way to pass closures through eval without leaking memory.
>
> Perhaps something like:
>
> (let [x 1
> f (fn [] x)
> f-sym (gensym)]
> (intern *ns* gensym (weak-ref f))
> (with-meta (eval `(fn [] (do-stuff-with @~f))) {::strong-ref f}))
>
> So that way f will be freed up when the resulting fn is gced.
>
> On 28 August 2013 17:59, Ben Wolfson <wolf...@gmail.com> wrote:
> > On Wed, Aug 28, 2013 at 9:27 AM, Jamie Brandon
> > <ja...@scattered-thoughts.net> wrote:
> >>
> >>
> >> If you aren't worried about leaking memory, a possible workaround is
> >> to intern the fn in some namespace and then put the symbol in the
> >> macro output.
> >
> >
> > Hrm, I hope it doesn't come to that---as long as I'm creating the
> functions
> > with their metadata, I can make things work, because I can add extra
> > information to the with-meta call or do extra things when making the
> call.
> > What I'd like, though, is for it to be possible to copy the metadata
> over to
> > a new function by client code, just using the regular (with-meta (fn
> [blah]
> > blah) (meta old-fn)) mechanism. But then the sneaky symbol, or whatever
> > extra thing, in the metadata, that's used in the form to be eval-ed is
> > pointing to the original function, not the one passed in. Maybe just
> > providing a utility for fixing up the metadata is the right move, though
> > it's kidn of dissatisfying.
> >
> >
> > --
> > Ben Wolfson
> > "Human kind has used its intelligence to vary the flavour of drinks,
> which
> > may be sweet, aromatic, fermented or spirit-based. ... Family and social
> > life also offer numerous other occasions to consume drinks for pleasure."
> > [Larousse, "Drink" entry]
> >
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--
Ben Wolfson
"Human kind has used its intelligence to vary the flavour of drinks, which
may be sweet, aromatic, fermented or spirit-based. ... Family and social
life also offer numerous other occasions to consume drinks for pleasure."
[Larousse, "Drink" entry]
--
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