Re: another question about exception safety
on Tue Mar 25 2008, acehreli-AT-gmail.com wrote:
On Mar 23, 10:23 pm, Mathias Gaunard <loufo...@gmail.com> wrote:
On Mar 24, 2:13 am, Mortiz <ydruga...@gmail.com> wrote:
Suppose some class has only two members: std::map<std::string,
std::string> member1 and std::string member2. Also it has ctor which
takes std::string and assigns it member2. In order to provide
exception-safe assignment operator for such class do I have to provide
non-throw swap method and use it inside assignment operator? How
should copy ctor look like
You can use the default copy constructor and assignment operator, they
will both be exception-safe.
Unfortunately no, the default assignment is not exception safe. The
default assigment assigns members and bases recursively. It doesn't
know how to revert if one of those operations throws. As a result, we
have a half-assigned object at hand.
Whether or not that can be considered exception-safe depends on whether
that "half-assigned" object meets its class invariants. If it does, the
default assignment operator gives the basic exception-safety guarantee.
Everyone seems to forget that the strong guarantee is neither always
necessary nor always sufficient for exception safety.
--
Dave Abrahams
BoostPro Computing
http://www.boostpro.com
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