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List:       boost
Subject:    Re: [boost] request for discussion - yet another approach to
From:       Larry Evans <cppljevans () suddenlink ! net>
Date:       2009-02-27 21:23:28
Message-ID: go9kvn$g9d$1 () ger ! gmane ! org
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On 02/27/09 14:13, Achilleas Margaritis wrote:
>> This seems a serious shortcoming.  To justify this, I guess you'd have
>> to somehow argue that this use-case doesn't happen very often or that
>> if it does, the user can easily detect that it happens and take
>> corrective active.  Then, to justify this method vs. the use of
>> weak-ptrs, you'd have to argue why it's easier for the user to detect
>> "transferred to a newer ptr" than it is to detect where a cycle is
>> created.
> 
> Indeed. I think the algorithm works for immutable ptrs only.
> 

Aren't mutable ptrs necessary for creating cycles?  Suppose
the ptr graph is B->A->B. (IOW, object B has pointer, B.ptr which points 
to object A, and object A has pointer, A.ptr which points to B.)
Now, either A or B must be created first.  When the first one is
created (suppose it's B)  it can't be constructed already pointing to A 
because A hasn't been created yet.  Consequently, B.ptr must be mutable 
in order to eventually point to A.

Am I missing something?


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