From: Frank Tao <dalfrank@...>
Date: 2008-12-04T04:59:15+09:00
Subject: Re: dynamic programming

Frank Tao wrote:
> # I have a class Adam
> # I want to modify the method("m_a") so that it will return the cached
> result
> # If no cached result is available, then return the original result
> # I want to create a class method(AKA: macro) to make it DRY
> #
> # So far, I have issues like
> # 1) dynmically define class variable
> # 2) failed to include a module inside a method of a class
> #
> # Any suggestion or comments will be appreciated
> #
> class Adam
>   def self.m_a
>     ["Adam#m_a"]
>   end
> end
> 
> class CachedAdam
>   caching_method :adam, :m_a
> 
>   def self.caching_method
>     # this method should do something to make the following codes
>   end
> end
> 
> 
> ## CachedAdam#caching_method should make and load the following codes
> #
> # module AdamWithCache
> #   def m_a_with_cache
> #     CachedAdam.get_cached_m_a || m_a_without_cache
> #   end
> #   def self.include(base)
> #     base.alias_method_chain :m_a, :cache
> #   end
> # end
> # Adam.class_eval{ include AdamWithCache }
> #
> # class CachedAdam
> #   def self.get_cached_m_a( adam_id )
> #     @@cache && @@cache[adam_id]
> #   end
> #
> #   def self.set_cached_m_a(hash_list)
> #     hash_list.each do |k,v|
> #       @@cache ||={}  # failed, any suggestion?
> #       @@cache[k] = v
> #     end
> #   end
> # end

THANKS FOR YOUR HELPFUL RESPONSE. I FOUND THAT MY ORIGINAL HAD SOME 
MISTAKES AND THEREFORE DID NOT REFLECT EXACTLY WHAT I WANT.
SO I UPDATE IT AS FOLLOWS:

class Adam
  def m_a
    "a"
  end
end

class CachedMethod
  @@cached_variables = {}

  def self.caching_method(model, method)
    model, method = model.to_s, method.to_s
    @@cached_variables["#{model}_#{method}_cache"] = {}

    (class << self; self; end).instance_eval do
      define_method "set_cached_#{model}_#{method}" do |hash_list|
        hash_list.each do |k,v|
          @@cached_variables["#{model}_#{method}_cache"][k] = v
        end
      end
      define_method "get_cached_#{model}_#{method}" do |model_id|
        @@cached_variables["#{model}_#{method}_cache"] &&
          @@cached_variables["#{model}_#{method}_cache"][model_id]
      end
    end


    #
    # Purpose: create a module and let it be included by Adam class
    # NOT WORKING, any suggestion?
    self.class_eval <<-EOD
     module AdamWithCache
       def m_a_with_cache
         CachedMethod.get_cached_adam_m_a(self.id) || m_a_without_cache
       end
       def self.include(base)
         base.alias_method_chain :m_a, :cache
       end
     end
     Adam.class_eval{ include AdamWithCache }
    EOD
  end

  def self.reset
    @@cached_variables = {}
  end

  self.caching_method :adam, :m_a

end

#module AdamWithCache
#  def m_a_with_cache
#    CachedMethod.get_cached_adam_m_a(self.id) || m_a_without_cache
#  end
#  def self.include(base)
#    base.alias_method_chain :m_a, :cache
#  end
#end
#Adam.class_eval{ include AdamWithCache }


#
#Example usage:
#=============================================

puts @adam_1 = Adam.new  #==> assume: @adam.id == 1
puts @adam_2 = Adam.new  #==> assume: @adam.id == 2
puts @adam_3 = Adam.new  #==> assume: @adam.id == 3
puts @adam_1.m_a         #==> "a"
puts @adam_2.m_a         #==> "a"
puts @adam_3.m_a         #==> "a"
puts @adam_1.id         #==> 1
puts @adam_2.id         #==> 2
puts @adam_3.id         #==> 3

hash_list = {@adam_1.id => "b", @adam_2.id => "c"}
CachedMethod.set_cached_adam_m_a(hash_list)
puts CachedMethod.get_cached_adam_m_a(@adam_1.id)  #==> "b"
puts @adam_1.m_a         #==> "b"    !!! DID NOT OUTPUT AS I EXPECTED
puts @adam_2.m_a         #==> "c"    !!! DIDO
puts @adam_3.m_a         #==> "a"    !!! DIDO

CachedMethod.reset
puts @adam_1.m_a         #==> "a"
puts @adam_2.m_a         #==> "a"
puts @adam_3.m_a         #==> "a"
-- 
Posted via http://www.ruby-forum.com/.