On 05.02.24 19:07, apoenitz wrote: > On Mon, Feb 05, 2024 at 09:36:39AM +0000, Marc Mutz via Development wrote: >> Hi, >> >> I've always understood it such that we as Qt must preserve the property >> that the hash for equal elements is equal within _one_ run of _one_ >> process. > > This would make debugging and testing of applications using QHash > less deterministic. > > There needs to ba some way to guarantee identical behavior of multiple runs > of the same binary. Setting the seed to 0 is currently such a way
You're right, my comment was overly simplistic. The non-determinism should be in the seed, and nowhere else. So developers should be able to rely on hash functions yielding the same value if the same seed is given _and the same Qt version is used_. That doesn't mean that applications or developers can rely on seed = 0 yielding the same hash value across Qt releases (even patch ones). The end result is the same, though: we can - definitely change exported qHash() functions - definitely _not_ change inline qHash() functions - possibly _not_ change any other qHash() function (there shouldn't be any in this category, but historically, there were some). Hope that clears it up. Thanks, Marc -- Marc Mutz <marc.m...@qt.io> Principal Software Engineer The Qt Company Erich-Thilo-Str. 10 12489 Berlin, Germany www.qt.io Geschäftsführer: Mika Pälsi, Juha Varelius, Jouni Lintunen Sitz der Gesellschaft: Berlin, Registergericht: Amtsgericht Charlottenburg, HRB 144331 B -- Development mailing list Development@qt-project.org https://lists.qt-project.org/listinfo/development
