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From: David Abrahams (dave_at_[hidden])
Date: 2004-03-07 08:42:43

Alberto Barbati <abarbati_at_[hidden]> writes:

> Suppose that T *is* assignable, is destroy+copy construction better
> than assignment? Probably no, for several reasons, including:
> 1) assigment is probably more efficient. In particular it might avoid
> destruction/reconstruction of sub-objects non related with the
> class invariant (for example: buffers, mutexes, etc.).
> 2) with the dtor/ctor idiom, if the ctor throws an exception, the old
> element is lost and you can't do anything about it, so the
> container cannot provide more than the basic guarantee for any
> method that might overwrite elements. However, the user might
> implement assigment with the strong guarantee, the container might
> leverage on that and provide the strong guarantee too at least for
> methods that might overwrite a single element such as
> push_back/push_front. (Of course, the user might implement
> assignment so badly that it doesn't provide even the basic
> guarantee and the container could not recover from that, but a
> library such not try to outsmart the user... too much ;).
> Just my opinion,

Well said.

Dave Abrahams
Boost Consulting

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