From: Sean O'Halpin <sean.ohalpin@...>
Date: 2005-11-04T07:33:13+09:00
Subject: Re: memoize and yaml

On 11/3/05, Daniel Berger <Daniel.Berger@qwest.com> wrote:
> Would folks like both options?  memoize_all or something?  Or just leave it alone?

With a slight adjustment, Florian's version can be used at the top
level too (at the cost of the instance variable @cache in main):

module Memoize
  def memoize(name)
    name = name.to_sym
    if self.to_s == "main"
      old_method = class<<self;self;end.instance_method(name)
      klass = Object
    else
      old_method = instance_method(name)
      klass = self
    end
    klass.send(:remove_method, name)
    klass.send(:define_method, name) do |*args|
      @cache ||= {}
      signature = [name] + args

      if @cache.include?(signature) then
        @cache[signature]
      else
        @cache[signature] = old_method.bind(self).call(*args)
      end
    end
  end
end

class D
  extend Memoize
  attr_accessor :value
  def initialize(value)
    @value = value
  end
  def t_memo(*args)
    puts "calculating #{args.inspect}"
    args.map { |x| x * value }
  end
  memoize(:t_memo)

end

d = D.new(10)
p d.t_memo(7,8)
p d.t_memo(7,8)

p d.t_memo(1,2)
p d.t_memo(1,2)

e = D.new(20)
p e.t_memo(1,2)
p e.t_memo(7,8)
p d.t_memo(7,8)

p d.instance_eval { @cache }

p e.instance_eval { @cache }

extend Memoize

def t_memo(*args)
  puts "calculating #{args.inspect}"
  args.map { |x| x * 5 }
end

memoize :t_memo

p t_memo(1,2,3)
p t_memo(1,2,3)
p t_memo(7,8)

p @cache


__END__
calculating [7, 8]
[70, 80]
[70, 80]
calculating [1, 2]
[10, 20]
[10, 20]
calculating [1, 2]
[20, 40]
calculating [7, 8]
[140, 160]
[70, 80]
{[:t_memo, 1, 2]=>[10, 20], [:t_memo, 7, 8]=>[70, 80]}
{[:t_memo, 1, 2]=>[20, 40], [:t_memo, 7, 8]=>[140, 160]}
calculating [1, 2, 3]
[5, 10, 15]
[5, 10, 15]
calculating [7, 8]
[35, 40]
{[:t_memo, 7, 8]=>[35, 40], [:t_memo, 1, 2, 3]=>[5, 10, 15]}

Regards,

Sean