From: Pit Capitain <pit@...>
Date: 2007-01-07T02:43:06+09:00
Subject: Re: cloning object with array members

Shea, you found your answer in the meantime, but I wanted to show you 
what was wrong with your other attempts:

>> a = MyClass.new
>> b = a.clone
>>
>> This method leaves 'b.arr1' pointing to the same data as a.arr1.

Yes, the default #dup and #clone create a shallow copy.

>> def clone
>>   rslt = super.clone
>> end
>>
>> This blows the stack, I believe because all methods are inherited 
>> virtually.

"super" isn't the same as in Java. super calls the same method of the 
superclass, so what you are doing here is:

   temp = super
   rslt = temp.clone

Since temp is an instance of MyClass, you're calling clone again, which 
gives you and endless recursion. The correct way would have been:

   def clone
     super
   end

But this obviously doen't help you.

>>   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.

The solution to this problem was:

>>   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.

And here, as you've noted yourself, you just forgot to return your new 
instance.

Regards,
Pit