On Tuesday, 16 September 2014 at 14:53:52 UTC, bearophile wrote:
Among the CppCon 2014 slide packs there is this nice one:
"Types Don't Know #", by Howard Hinnant:
https://github.com/CppCon/CppCon2014/tree/master/Presentations/Types%20Don%27t%20Know%20%23%20-%20Howard%20Hinnant%20-%20CppCon%202014
It shows a nice idea to perform transitive hashing in a
flexible and efficient way. Perhaps the idea can be used in D
too. It suggests the introduction of a hashAppend standard
method.
Yes, I've never understood why std::hash was designed the way it
is. Or why allowing the user to supply a seed value seems to be
unusual for publicly available hash routines (which is basically
what Howard has proposed). rt.util.hash.hashOf accepts a seed
value, and any hash routine we made publicly callable should as
well. Not to do so is really pretty useless.
I guess this also has implications for composite types in D. If
I have a class that references other classes, I might want to do
the same basic thing. In which case, calling Object.toHash isn't
sufficient as it fails in the same manner. I suppose we really
need to extend toHash to accept an optional seed value as well.
