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comp.lang.ruby

changing array values

Andrew Salveson

4/13/2009 8:42:00 PM

What I'd like is an array of objects, each of which contains an array of
integers, and each successive object in the array should contain a
slightly different array of integers than the previous object.

For some reason, when I run the code below:

class TEST
def initialize(args)
@args = args
end
def describe
return @args.join(", ")
end
end


def test
old = [0,0,0,0,0,0]
tests = []
5.times do |i|
new = old
new[rand(old.size)] = rand(5) # randomly changes one of the members
of the array to a number from 0 to 4
tests[i] = TEST.new(new)
puts tests[i].describe
end
return tests
end

I get this output:

0, 0, 0, 0, 0, 0
0, 0, 0, 0, 0, 1
0, 0, 0, 0, 0, 4
0, 0, 0, 2, 0, 4
0, 0, 1, 2, 0, 4
[#<TEST:0x3f3d9f0 @args=[0, 0, 1, 2, 0, 4]>,
#<TEST:0x3f3d9d8 @args=[0, 0, 1, 2, 0, 4]>,
#<TEST:0x3f3d900 @args=[0, 0, 1, 2, 0, 4]>,
#<TEST:0x3f3d828 @args=[0, 0, 1, 2, 0, 4]>,
#<TEST:0x3f3d750 @args=[0, 0, 1, 2, 0, 4]>]

As you can see, each object in the object array contains the last array
of integers, even though the objects are being initialized with
different arrays of integers.

Strangely enough, if I use a single integer everywhere I here use an
array, everything works just fine.

I cannot for the life of me figure out why this is happening and would
be extremely grateful it if someone could enlighten me . . .
--
Posted via http://www.ruby-....
2 Answers

James Coglan

4/13/2009 8:46:00 PM

0

[Note: parts of this message were removed to make it a legal post.]

> For some reason, when I run the code below:
>
> class TEST
> def initialize(args)
> @args = args
> end
> def describe
> return @args.join(", ")
> end
> end
>
>
> def test
> old = [0,0,0,0,0,0]
> tests = []
> 5.times do |i|
> new = old
> new[rand(old.size)] = rand(5) # randomly changes one of the members
> of the array to a number from 0 to 4
> tests[i] = TEST.new(new)
> puts tests[i].describe
> end
> return tests
> end
>
> I get this output:
>
> 0, 0, 0, 0, 0, 0
> 0, 0, 0, 0, 0, 1
> 0, 0, 0, 0, 0, 4
> 0, 0, 0, 2, 0, 4
> 0, 0, 1, 2, 0, 4
> [#<TEST:0x3f3d9f0 @args=[0, 0, 1, 2, 0, 4]>,
> #<TEST:0x3f3d9d8 @args=[0, 0, 1, 2, 0, 4]>,
> #<TEST:0x3f3d900 @args=[0, 0, 1, 2, 0, 4]>,
> #<TEST:0x3f3d828 @args=[0, 0, 1, 2, 0, 4]>,
> #<TEST:0x3f3d750 @args=[0, 0, 1, 2, 0, 4]>]



When you set 'new = old', you're just creating another reference to the same
array. To copy the array, use 'new = old.dup'. (dup = duplicate)

Andrew Salveson

4/13/2009 8:52:00 PM

0

James Coglan wrote:
>>
>> end
>> [#<TEST:0x3f3d9f0 @args=[0, 0, 1, 2, 0, 4]>,
>> #<TEST:0x3f3d9d8 @args=[0, 0, 1, 2, 0, 4]>,
>> #<TEST:0x3f3d900 @args=[0, 0, 1, 2, 0, 4]>,
>> #<TEST:0x3f3d828 @args=[0, 0, 1, 2, 0, 4]>,
>> #<TEST:0x3f3d750 @args=[0, 0, 1, 2, 0, 4]>]
>
>
>
> When you set 'new = old', you're just creating another reference to the
> same
> array. To copy the array, use 'new = old.dup'. (dup = duplicate)


Ahh, fantastic! Thank you.
--
Posted via http://www.ruby-....