From: Gary Weaver <lists@...>
Date: 2012-11-29T19:56:59+09:00
Subject: Re: Need advice- would like to implement a delayed-load proxy class

> That part is easy, as I've done similar in my constance gem.

Sorry, I meant the classmeta gem: 
https://github.com/garysweaver/classmeta

Been thinking more about this, and although I still think it is a 
somewhat horrid idea, I thought of some tweaks:

class FlyweightProxy < BasicObject
  def initialize(const_name)
    @@name = const_name
  end

  def method_missing(meth, *args, &block)
    remove_class_variable(:@@name)
    # really load class or get instance, and then call method on it
    SomeAutoloader.get(@@name).send(meth, *args, &block)
  end
end

# this is not to be taken literally. for example, in classmeta I 
overrode the method called in Rails autoloading via alias_method'ing and 
redefining load_missing_constant, which I might have just been able to 
do via defining load_missing_constant and calling super instead, but 
don't remember if I tried that: 
https://github.com/garysweaver/classmeta/blob/master/lib/classmeta/dependencies.rb

module ModuleConstMissing
  def const_missing(const_name)
    FlyweightProxy.new(const_name)
  end
end

Module.class_eval { include ModuleConstMissing }

But, I'm not sure if that would work (need to test).

Sorry if this is way too poorly thought out. Just looking for ideas, 
mostly.

Gary Weaver wrote in post #1086999:
> I'd like to have const_missing return a class that would do the
> following:
>
> 1. Have the same class name as the class it should have loaded but
> without loading the class. Let's call this "proxy".
>
> That part is easy, as I've done similar in my constance gem. Here is
> where it starts to get more difficult:
>
> 2. Implement method missing such that when "proxy" is called it in turn
> calls another class that unloads the proxy class and then loads the
> originally requested file.
>
> Implementing method missing is easy, and removing a constant not hard
> either, but how can an unloaded class return something from method
> missing when it is gone? That wouldn't work.
>
> So then you might say "of course not, just use method missing and return
> from the proxy", but if possible I don't want to have the "proxy" class
> act as a wrapper or delegate all calls because that is additional
> overhead. Maybe it would be ok and transparent and I could mess with the
> caller stack to make it appear as if the proxy were not even there, but
> I think eventually the magic go-between wrapper would be a problem.
>
> This actually isn't an academic question- I was trying to think of a
> solution to the problem of people using names of classes rather than the
> constants in class bodies where associations, etc. are defined in Rails
> (note: this is not a Rails question, but yes that is where I'd like to
> use it). By returning a flyweight proxy class that loads and calls the
> real class as needed, they wouldn't need to use strings instead of
> classnames because const_missing would return something that didn't get
> into some sort of massive autoloading disaster that the community is
> afraid of.
>
> Sorry if this just sounds idiotic.

-- 
Posted via http://www.ruby-forum.com/.