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From "Senaka Fernando" <>
Subject Re: Issue in using 'detach' for cloning
Date Sat, 16 Feb 2008 10:35:37 GMT

That is an ideal solution in testing this and getting our implementations
straight, without ever having to worry about side effects. +1


> wrote:
>> Dinesh, you are right that one can develop a cloning algorithm that
>> defers any copying until the object is modified, a copy-on-write
>> algorithm.  But such an algorithm would depend on knowing that ref
>> counts are used only for cloning.  Given this assumption, when the ref
>> count was greater than one, the code could choose to copy an instantiate
>> a new instance of the object when it was modified.
>> I don't think that assumption is met today.  I see ref counts
>> implemented currently for attributes and namespaces, and not for
>> elements or text.  In particular, for attributes, this allows the user
>> of axiom to create an attribute one time, and attach it to several
>> elements as needed.  And it could be that this user wants the ability to
>> change the attribute value once and have the modification apply to all
>> the elements that share it.
>> Now maybe this is a capability that was not foreseen and is not
>> supported, but it exists nonetheless.  So one cannot implement a
>> copy-on-write algorithm without risking breaking existing code.
> Given the chances of breaking the existing - shall we do this change on
> a temporary branch, rather than on the svn head?
> This way, we have more room for taking risks and fixing breaks.
> Thanks,
> Samisa...
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