Forum: Ruby saving values in block problem

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Peng Zuo (Guest)
on 2009-05-26 19:45
(Received via mailing list)
Hi,I'm using ruby 1.87. this problem seems to be the block context bug
for
1.8x, in the results array, I always got the same value, which is the
last
return value of the iteration .
I've got an object, which has multiple states. when I call each_state,
I'm
actually changing the state.

results = []
an_object.each_state do |the_object|
    #some manipulations
    results << the_object
end

the each_state method looks like:

def each_state
    #blah blah, change the current state
    yield(self)   # I also tried self.dup, but it didnt work either.
end

anyone knows how to solve this?
TIA

Regards,

Peng Zuo
Joel VanderWerf (Guest)
on 2009-05-26 20:58
(Received via mailing list)
Peng Zuo wrote:
> end
>
> the each_state method looks like:
>
> def each_state
>     #blah blah, change the current state
>     yield(self)   # I also tried self.dup, but it didnt work either.
> end

I'm guessing what you want is for results[i] to be a snapshot of the
object as it is in the i-th state?

If dup doesn't work, maybe your object has some other objects attached
to it in which you are storing something? In that case, try a deep copy:

Marshal.load(Marshal.dump(self))
Brian C. (Guest)
on 2009-05-27 01:18
Peng Zuo wrote:
> Hi,I'm using ruby 1.87. this problem seems to be the block context bug

http://www.catb.org/~esr/faqs/smart-questions.html#id306810

Does this explain what you are seeing?

irb(main):001:0> a = []
=> []
irb(main):002:0> str = "xxx"
=> "xxx"
irb(main):003:0> a << str
=> ["xxx"]
irb(main):004:0> str << "yyy"
=> "xxxyyy"
irb(main):005:0> a << str
=> ["xxxyyy", "xxxyyy"]
irb(main):006:0> str << "zzz"
=> "xxxyyyzzz"
irb(main):007:0> a << str
=> ["xxxyyyzzz", "xxxyyyzzz", "xxxyyyzzz"]
irb(main):008:0> a
=> ["xxxyyyzzz", "xxxyyyzzz", "xxxyyyzzz"]
irb(main):009:0>

An array only holds references to objects. If you insert a reference to
the same object multiple times into the array, then you will simply see
the same object multiple times.

As for why 'dup' doesn't work: you'll need to show your code. If you are
maintaining state in an instance variable, dup should work. If you are
maintaining state indirectly - the instance variable points to some
other object which in turn holds state - then the dup'd object will
still point to this same object.
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