On 12/7/24 03:23, Ivan Matek wrote:
On Sat, Dec 7, 2024 at 1:08 AM Andrey Semashev via Boost <boost@lists.boost.org <mailto:boost@lists.boost.org>> wrote:
On 12/7/24 01:42, Ivan Matek wrote: > > > On Fri, Dec 6, 2024 at 10:36 PM Andrey Semashev via Boost > <boost@lists.boost.org <mailto:boost@lists.boost.org> <mailto:boost@lists.boost.org <mailto:boost@lists.boost.org>>> wrote:
As to the usage with the forced move, I don't think the added complexity is justified. If the goal is to make sure the hash value doesn't change upon successive calls to result() (to use the existing nomenclature)
Goal was to "encourage" users in 2 ways to call result() only once. First way is that move signals that value is "tainted", second is that clang-tidy can detect double moves sometimes.
But I don't see the benefit in introducing UB (potentially, to be caught by sanitizers - *if* one runs one) upon subsequent calls to result().
If you are referring to multiple calls to get_digest(std::move(h)); There is no UB. Move is just a cast, we do not nuke the member when we return it's result(), and clang-tidychecks are static(not runtime).
It may be UB if the hasher's result() has an rvalue-qualified overload that moves parts of its internal representation out in the returned hash value.