Hi Tim, thanks for the answer. I wasn't talking about Image specifically,
but that's an interesting way to flexibly store all the memos. Is that your
general go-to solution, have a properties dictionary inside each object? It
feels more like a Python solution than Julia, but it makes a lot of sense
for medium-to-large objects.
On Monday, August 31, 2015 at 4:34:38 AM UTC-4, Tim Holy wrote:
>
> Re Image (assuming you mean the Image from Images.jl), you can just add a
> "hash" property---no recreation/redesign needed. Wouldn't necessarily have
> to
> be a nullable, either. For efficiency, Images implements a `@get` macro,
> so
>
> @get img "hash" hashfunc(img)
>
> would:
> - extract the stored "hash" property, if it already exists, without
> computing
> hashfunc(img)
> - compute and create the "hash" property, if it doesn't exist
>
> --Tim
>
> On Sunday, August 30, 2015 10:04:26 PM Cedric St-Jean wrote:
> > I tend to use memoization heavily in my mostly-functional code.
> Memoize.jl
> > is neat, but it doesn't use a WeakKeyDict.
> >
> > 1. Is there any specific reason for that? Won't that code just hog the
> > objects forever?
> >
> > 2. In SBCL, weak dictionaries and weak references had terrible O(N²)
> > performance (I could never understand why), is that also the case for
> Julia?
> >
> > 3. In many cases, it makes more sense to store the memoized value inside
> > the object's field (for instance, storing the hash for an image). That
> will
> > be a good place to use Nullable, right?
> >
> > # Obviously I don't mean to recreate Image specifically
> > type Image
> > ...
> > hash_value::Nullable{int}
> > end
> >
> > function hash(img::Image)
> > if isnull(img.hash_value)
> > return img.hash_value = ...
> > else
> > return get(img.hash_value)
> > end
> > end
> >
> > 4. I still don't have the hang of Julia macros. In Common Lisp, I could
> > easily write my own
> > (defstruct* Image
> > ... normal fields
> > (cache hash))
> > and have the above code automatically generated. What's the best syntax
> to
> > use with Julia? Something like
> > @type_cached Image begin
> > ...
> > cache(hash)
> > end
> >
> > function hash_impl(img::Imaeg)
> > ...
> > end
> > ? I don't like much how the `begin` makes it stick out, whereas Common
> > Lisp's version is much more seamless. Isn't there a way to tell the
> parser
> > "keep reading this macro until `end`" without having a begin statement?
> >
> > Is there a better, more native solution to this problem?
> >
> > Cédric
>
>
