From: Anders Borch <ruby@...>
Date: 2004-06-17T19:28:51+09:00
Subject: Re: Delayed Instantiation - delayed.rb

is it just me, or could the same results come from this:

class DelayedInstance
   def initialize(klass,*args)
     @klass = klass
     @args = args
     @object = nil
   end

   def method_missing(meth,*args,&block)
     @object = @klass.send(:new,*@args) if @object.nil?
     @object.send(meth,*args,&block)
   end
end



matt wrote:
> Here's some code I wrote to delay object instantiation until an
> object's methods are needed.  If there's anything fooey about it, or
> if there's a better version out there, please let me know :-)
> 
> 
> 
> --begin--
> #########################################################################
> #########################################################################
> #### delayed.rb:  Thunks for Object Insantiation                    
> ####
> #### Author:  Matthew Maycock                                       
> ####
> #### Email:   _mr_bill_98@yahoo.com                                 
> ####
> #### Date:    June 16th, 2004 AD!                                   
> ####
> ####                                                                
> ####
> #### Purpose:                                                       
> ####
> ####    Delay instantiation of objects until needed.                
> ####
> ####    Overhead given by an extra indirection of dispatch          
> ####
> ####    Use at your own risk!                                       
> ####
> ####                                                                
> ####
> #### License:                                                       
> ####
> ####    The least restrictive license applicable to this software   
> ####
> ####    given that it was written in ruby and uses the ruby library.
> ####
> ####    I don't really know that much about such things, so if there
> ####
> ####    isn't anything in the way, consider this released under the 
> ####
> ####    public domain, free for all!                                
> ####
> #########################################################################
> #########################################################################
> 
> 
> 
> # Delay creation of an object until some method tries to use it.
> class DelayedInstance < Object
>   def initialize(klass, *args)
>     @object  = Object.new
>     ivars = Object.instance_method(:instance_variables)
>     ieval = Object.instance_method(:instance_eval)
>     iclss = Object.instance_method(:class)
>     inspt = Object.instance_method(:inspect)
> 
>     switched = @delayed_switched = false
> 
> 
>     switch = @delayed_switch     = Proc.new {
>       raise "Already switched!" if switched
>       switched = @delayed_switched = true
>       @object  = klass.send(:new, *args)
>     }
> 
>     delayed_self = self
>     @object.instance_eval {
>       @delayed_parent = delayed_self
>       @delayed_switch = switch
>       @delayed_added  = false
>       @delayed_eval   = ieval
>     }
> 
>     [:==, :===, :=~, :__id__, :__send__, :class, :clone, :display,
> :dup, :eql?, :equal?, :extend, :freeze, :frozen?, :hash, :id,
>      :inspect, :instance_eval, :instance_of, :instance_variable_get,
> :instance_variable_set, :instance_variables, :is_a?, :kind_of?,
>      :method, :methods, :new, :nil?, :object_id, :private_methods,
> :protected_methods, :public_methods, :remove_instance_variable,
>      :respond_to?, :send, :singleton_method_added,
> :singleton_method_removed, :singleton_method_undefined,
> :singleton_methods, :taint,
>      :tainted?, :to_a, :to_s, :type, :untaint].each {|sym|
>       eval <<-END_EVAL
>         def @object.#{sym.to_s}(*args, &block)
>           return super(*args, &block) unless @delayed_added
>           parent = @delayed_parent
>           @delayed_switch[]
>           obj    = @delayed_eval.bind(parent).call { @object }
>           obj.send(#{sym.inspect}, *args, &block)
>         end
>       END_EVAL
>     }
> 
>     Object.instance_method(:instance_eval).bind(@object).call
> {@delayed_added = true}
>   end
> 
>   def method_missing(sym, *args, &block)
>     @delayed_switch[] unless @delayed_switched
>     @object.send(sym, *args, &block)
>   end
> end
> 
> [:==, :===, :=~, :__id__, :__send__, :class, :clone, :display, :dup,
> :eql?, :equal?, :extend, :freeze, :frozen?, :hash, :id,
>  :inspect, :instance_eval, :instance_of, :instance_variable_get,
> :instance_variable_set, :instance_variables, :is_a?, :kind_of?,
>  :method, :methods, :new, :nil?, :object_id, :private_methods,
> :protected_methods, :public_methods, :remove_instance_variable,
>  :respond_to?, :send, :singleton_method_added,
> :singleton_method_removed, :singleton_method_undefined,
> :singleton_methods, :taint,
>  :tainted?, :to_a, :to_s, :type, :untaint].each {|sym|
>   DelayedInstance.module_eval <<-END_EVAL
>     def #{sym.to_s}(*args, &block)
>       @object.send(#{sym.inspect}, *args, &block)
>     end
>   END_EVAL
> }
> 
> 
> 
> if __FILE__ == $0 then
> 
>   class Test
>     def initialize(index)
>       $stdout.puts "Something that takes a thousand hours..."
>       @index = index
>     end
> 
>     def display
>       $stdout.puts @index
>     end
>   end
> 
>   data = (1..10).map {|i| DelayedInstance.new(Test, i)}
>   data.each {|d| d.display}
> 
>   $stdout.puts
>   foo = DelayedInstance.new(Test, 1000)
>   foo.instance_eval {
>     $stdout.puts "Instance Eval!"
>     @santa = 100
>   }
> 
>   $stdout.puts foo.instance_variables.inspect
>   $stdout.puts foo.instance_eval {@santa}
> end
> 
> =begin
> ### ruby -v:  ruby 1.8.1 (2003-12-25) [i386-mswin32]
> # OUTPUT
> Something that takes a thousand hours...
> 1
> Something that takes a thousand hours...
> 2
> Something that takes a thousand hours...
> 3
> Something that takes a thousand hours...
> 4
> Something that takes a thousand hours...
> 5
> Something that takes a thousand hours...
> 6
> Something that takes a thousand hours...
> 7
> Something that takes a thousand hours...
> 8
> Something that takes a thousand hours...
> 9
> Something that takes a thousand hours...
> 10
> 
> Something that takes a thousand hours...
> Instance Eval!
> ["@index", "@santa"]
> 100
> =end
>