Re: [boost] Review: Special functions, Quaternions, Octonions

From: David Abrahams (abrahams_at_[hidden])
Date: 2001-05-18 11:45:47

----- Original Message -----
From: "Gary Powell" <Gary.Powell_at_[hidden]>

>   Also, while I can see that it would not generate the most efficient
code,
> I have a tendency to write templated assignment operators as
>
>   octonion temp(a_affecter);
>   using std::swap;
>   swap(temp, *this);
>   return this;
>
> which is exception safe, but makes an extra temporary copy.

The other way is exception-safe also. People always mistakenly associate
exception-safety with the strong guarantee. In many cases the strong
guarantee is neither sufficient nor often even neccessary for writing
exception-safe programs. The most we should say about the above method is
that it "gives stronger exception-safety guarantees than the other way,
assuming swap is non-throwing".

Before suggesting that all assignments should be written that way by default
it is worth considering whether the strong guarantee will pay off for the
class in question.

-Dave