From: Shea Martin <shea@...>
Date: 2007-01-07T00:45:10+09:00
Subject: Re: cloning object with array members

Shea Martin wrote:
> Consider a simple class like this:
> class MyClass
>   def initialize
>     @var1 = ''
>     @arr1 = []
>   end
> end
> 
> 
> Now if I have an instance of MyClass, and want to clone it, what is the 
> 'cleanest' way to do this?
> 
> a = MyClass.new
> b = a.clone
> 
> This method leaves 'b.arr1' pointing to the same data as a.arr1.
> 
> Hmmm... I'll try overriding clone, and manually deal with the arrays:
> 
> def clone
>   rslt = super.clone
> end
> 
> This blows the stack, I believe because all methods are inherited 
> virtually.
> 
> Ok, so now I have to manually copy everything in clone, whatever, I am 
> getting sick of this:
> 
>   def clone
>     rslt = MyClass.new
>     rslt.var1 = @var1
>     rslt.arr1 = @arr1.clone
>     rslt
>   end
> 
> Turns out this does not compute either, as there is no method var1= or 
> arr1= ! I want to keep var1 private, so can't go this route either.
> 
> 
> One more attempt:
>   def clone
>     rslt = MyClass.new
> 
>     self.instance_variables.each do |member|
>       rslt.instance_variable_set( member, 
> self.instance_variable_get(member).clone )
>     end
>   end
> 
> This fails as the methos do not seem to copy over.
> 
> There has to be a simple way to do something like this?  What is common 
> recipe for something like this?   Should this really be that hard in ruby?
> 
> ~S


Thanks for all the help.  My last attempt at clone turns out to be fine, 
I just forgot to return 'rslt'.  That fixed everything.

~S