Re: [hash2] Difference from paper: HashAlgorithm interface vs. function object

From: Ivan Matek (libbooze_at_[hidden])
Date: 2024-12-12 01:40:33

On Wed, Dec 11, 2024 at 6:32 PM Peter Dimov via Boost <boost_at_[hidden]>
wrote:

> hash_append_unordered_range should be seen as representative
> of what users may need to do with hash algorithms, and it clearly
> demonstrates that sometimes, taking a copy of the hash algorithm is
> needed.
>
>

Can you please elaborate why is this necessary(not speaking generally, just
in this particular case)?
I originally though we do
    Hash h2( h );
so that seed of h matters, but  then I noticed that anyway at the end of
function we do
    hash2::hash_append( h, f, w );
    hash2::hash_append_size( h, f, m );
so for I presume seed of h matters even if we default constructed hashers
in the loop.