On Fri, Nov 16, 2007 at 09:05:48AM +0900, Miles Bader wrote:
Colin <share-lua@think42.com> writes:
I would guess that one of the reasons of the missing __hash meta
event is
that it's not that easy to design -- how do you make sure that
the __hash
meta event is "compatible" with the Lua hash function and the
other table
internals?
Not to mention a non-negligible speed hit in a rather critical
area of
Lua! Making table lookups slower makes _everything_ slower.
(As long as its not slower than the workarounds ... for me, the
suggestion
of creating caches of all userdata objets to reuse the same when
whenever
one with the same value is needed does not sound too good because
in my
application typically much more userdata objects are created than
are used
for table lookups.)
It would probably be much more acceptable if user-defined __hash
hooks
were only used for tables with some flag turned on (which could be
tested very quickly in the C core), with that flag defaulting to off.
Hm, this, and the suggestion of using the index/newindex
metamethods does
not work for me either because I want the mechanism to work by
default,
however it gave me the following idea:
How about a flag on every userdata object that switches between the
current
pointer-based hashing for tables, and one that uses the actual
userdata (of
which the address and length is known) i.e. one could use the same
hashing
as for strings, and memcmp() for the equality check)?
Regards, Colin
