Simple newbie question


#1

Hi,
I have a piece of code below in which I;
1…make a new NumberList object and append two MyNumber objects.
2…copy the NumberList object and append a further MyNumber object.
However after this both objects are the same.
Any help would be greatly appreciated.
Thanks,
Kieran


class MyNumber
def initialize(x)
@x=x
end
attr_accessor :x
end
class MyNumberList
def initialize
@nums = Array.new
end
def append(num)
@nums.push(num)
self
end
def sum
sum=0
@nums.each {|s| sum += s.x }
return sum
end
end

zl1=MyNumberList.new; zl1.append(MyNumber.new(10));
zl1.append(MyNumber.new(20))
puts zl1.sum
zl2=zl1; zl2.append(MyNumber.new(40))
puts zl1.sum
puts zl2.sum


#2

Hi –

On Thu, 26 Jan 2006, kieran kirwan wrote:

Hi,
I have a piece of code below in which I;
1…make a new NumberList object and append two MyNumber objects.
2…copy the NumberList object and append a further MyNumber object.
However after this both objects are the same.
[…]
zl2=zl1

That’s why they’re the same: by doing this assignment, you’re storing
a new reference to the object in zl2. But it’s still the same object.

David


David A. Black
removed_email_address@domain.invalid

“Ruby for Rails”, from Manning Publications, coming May 1, 2006!


#3

kieran kirwan removed_email_address@domain.invalid writes:

Hi,
I have a piece of code below in which I;
1…make a new NumberList object and append two MyNumber objects.
2…copy the NumberList object and append a further MyNumber object.
However after this both objects are the same.
Any help would be greatly appreciated.

See http://www.rubygarden.org/ruby?Make_A_Deep_Copy_Of_An_Object

zl2=zl1;

As said, you doesn’t copy the contents of zl1 in zl2: you make zl2 and
zl1 reference the same objet. What you want to do is to copy the
contents of zl1 into zl2.