From: Francis Hwang <sera@...>
Date: 2004-12-04T03:56:59+09:00
Subject: Re: how to create an object of a class you don't know yet

"new" is just a class method, and you can call class methods on classes 
that aren't bound at the time of interpretation. For example:

instance = MyClass.new

is the same as

a_class = MyClass
instance = a_class.new

So you can do things like:

irb(main):001:0> classes = [ String, Hash, Array ]
=> [String, Hash, Array]
irb(main):002:0> grab_bag = classes.collect { |a_class| a_class.new }
=> ["", {}, []]



On Dec 3, 2004, at 1:44 PM, Bradley, Todd wrote:

> Hi, I'm just now getting into Ruby's OO-ness, and could use some 
> advice.
> I'm trying to create an object, but which specific class needs to be
> determined at runtime.  I figured out how to do this by creating a
> string and executing it using the "eval" command, but I know there must
> be an easier way.  My first guess was to do something like 
> #{answer}.new
> but that didn't work.
>
>
> Here's my code:
>
>
> class Foo
> 	def method1
> 	end
> end
>
> class Bar
> 	def method2
> 	end
> end
>
> # Pretend this was determined at runtime
> answer = "Foo"
>
>
> # There must be a better way of doing this:
>
> myobj = Object.new # Needs to exist in this scope
> mystring = "myobj = #{answer}.new"
>
> eval mystring
>
> puts "I just created a #{myobj.class} object."
>
>
>
>
> Any advice is appreciated.  Thanks in advance!
>
>
> Todd.
>
>

Francis Hwang
http://fhwang.net/