From: "Shot (Piotr Szotkowski)" <shot@...>
Date: 2008-02-20T01:01:30+09:00
Subject: Object#freeze as a basis for caching of method results?

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Hello, ruby-talk.

After profiling my code I figured out I might want to attempt some
caching of results obtained in =E2=80=98heavy=E2=80=99 methods. Is there an=
 idiomatic
way to do method-results caching in Ruby?

The first thing that came to my mind as a mean to ensure the cache=E2=80=99s
=E2=80=98freshness=E2=80=99 is to freeze the object in question. Does this =
make sense?

For example, assume that a Blanket is a Set of Blocks, and
that there=E2=80=99s a computation-intesive method =E2=80=98separations=E2=
=80=99:



class Blanket < Set

  def separations
    seps =3D Set[]
    # some =E2=80=98heavy=E2=80=99 code that builds seps
    seps
  end

end



Would the below make sense?



class Blanket < Set

  def freeze
    each { |block| block.freeze }
    super
  end

  def separations
    return @seps if @seps
    @seps =3D Set[]
    # the =E2=80=98heavy=E2=80=99 code from that builds @seps this time
    freeze
    @seps
  end

end



I guess my question boils down to what does exactly Object#freeze
prevent from being modified =E2=80=93 simply all the properties?

If so, does it mean I can only have one method like the above (because
if some other method did any freezing, I couldn=E2=80=99t initialise the @s=
eps
cache when the first call to separations occurs)?

Is there any =E2=80=98best practice=E2=80=99 in Ruby
with regards to caching method results?

Is there any obvious other approach to such caching? (I thought about
having a @cache instance variable that would get reset on object
changes, but I=E2=80=99m not sure how to obtain all the list of methods that
can change an object =E2=80=93 i.e., methods that throw error when a given
object is frozen.)

Thanks in advance for any replies/suggestions/insights!

-- Shot
--=20
Q is for quota, a Berkeley-type fable, and
R is for ranlib, for sorting ar table.
S is for spell, which attempts to belittle, while
T is for true, which does very little.

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