Saving values in block problem


#1

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


#2

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))


#3

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.