From: 7stud -- <bbxx789_05ss@...>
Date: 2009-02-28T12:31:59+09:00
Subject: Re: Marshal.load does not create new instances?

Ian Trudel wrote:
> Marshal does not seem to instantiate given class(es) on load. Moreover,
> it will absolutely work as long as the class is define
>

Seems pretty standard across programming languages.

> 
> This is really annoying considering that I would like to load data onto
> one (among many) version of Data class. The version of the class to be
> used is determined and set at run-time according to the file loaded;
> this is my ultimate goal. 
> 
> Any suggestions?
> 

How about something like this:

-----------
#a program that dumps an object:

class MyData
  def greet
    puts "hello"
  end
end

d = MyData.new
File.open("def1.txt", "w") do |f|
  Marshal.dump(d, f)
end
------------

#program that loads the objects:

def1 = <<-def1
  class MyData
    def greet
      puts "hello"
    end
  end
def1

def2  = <<-def2
  class MyData
    def greet
      puts "goodbye"
    end
    def shout
      puts "HEY"
    end
  end
def2

def3 = <<-def3
  class MyData
    def greet
      puts "last class"
    end
    def cry
      "Wahhhh wahhh"
    end
  end
def3

data_classes = {
  "def1" => def1,
  "def2" => def2,
  "def3" => def3
}

print "Enter file name: "
fname = gets.chomp
defname = fname.split(".")[0]
eval(data_classes[defname])

begin
  File.open(fname) do |f|
    d = Marshal.load(f)
    d.greet
    d.shout
    d.cry
  end
rescue NoMethodError
  #do nothing
ensure
  f.close unless f.nil?
end

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