Re: [boost] [hash][array][stacktrace][type_index] Adding noexcept to hash

Subject: Re: [boost] [hash][array][stacktrace][type_index] Adding noexcept to hash
From: Richard Hodges (hodges.r_at_[hidden])
Date: 2017-12-04 09:22:26

On 4 December 2017 at 09:57, Daniel James via Boost <boost_at_[hidden]>
wrote:

> On 4 December 2017 at 06:54, Richard Hodges via Boost
> <boost_at_[hidden]> wrote:
> > Adding a noexcept specification (i.e. making an interface more
> restrictive)
> > sounds like a breaking change to me. Although it's the correct thing to
> do,
> > surely anyone who has an override of hash_range in their code will be
> > affected?
>
> It isn't a member function, so there's no way to override it. The
> customization point is a call to hash_value via argument dependent
> lookup. The noexcept specifiers are going to be conditional on whether
> the iterators and hash functions are noexcept, so if an overload
> doesn't have a noexcept specification, then hash_range for that value
> is going to be effectively noexcept(false) and will still be
> compatible.
>
> Forgive me. I of course meant overload.

What I mean is that I assume the intention is to make any hashable thing
noexcept-hashable? That seems sensible to me, since the hash of an object
is an invariant for any given state of the object in any one program run.

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