Re: How on earth did noexcept get through the standards process?
On Mar 14, 11:31 pm, itaj sherman <itajsher...@gmail.com> wrote:
On Mar 14, 8:17 pm, Andrew <marlow.and...@gmail.com> wrote:
I have just come across the new noexcept feature and I am horrified.
So why on earth do we have noexcept? And given that it is there, why
are the checks not strict? It is the lack of strictness that seems to
be causing the controversy, i.e. undefined behaviour versus
std::terminate. I reckon the answer is that old chestnut, premature
optimization is the root of all evil.
Discuss!
There are two main different kinds of "exception specification" for a
function:
1) "requests" - the programmer requests the compiler to verify that
the function applies to them (in some certain defined ways at compile
and/or runtime).
2) "promises" - the programmer promises that the function applies,
allowing the compiler to assume so for whatever it does (that can help
exception safety concept checking, and optimization).
The old specifications where of the first kind, and for
various reasons many people concluded they do more harm then
good (especially for performance critical languages).
Actually, the performance impact on most platforms was zero.
The noexcept is of the second kind. More specifically, allowing only a
yes/no specification rather than exception type specific. The
programmer promises that the function throws nothing, the compiler is
allowed to assume so for whatever it does. The implementation is also
allowed to check that if they want, but generally they don't have to
do so, so that they don't cause unnecessary runtime overhead.
In other words, the introduce yet another case of undefined
behavior. I've not looked at them in detail, but if that's the
case, I'm against them.
The old ones actually worked pretty well. They provided perhaps
more than was needed---it's hard to think of a case where
anything other than throw() was appropriate. But at least when
you wrote throw(), you had a guarantee.
--
James Kanze
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