Doh! You're right of course, how silly not to notice it before - the
break out test is completely stupid. (I guess in the back of
my mind I must have thought the values were coming out in order -
which of course they are not). It breaks out very early
and that explains why it's so much faster.
If I change the test to >400000 (which gets me about 3/4
through the hash) then I get the following results...
Benchmark: timing 1000 iterations of each, keys...
each: 2 wallclock secs ( 2.39 usr + 0.00 sys = 2.39 CPU) @ 418.41/s (n=1000)
keys: 2 wallclock secs ( 2.23 usr + 0.00 sys = 2.23 CPU) @ 448.43/s (n=1000)
Rate each keys
each 418/s -- -7%
keys 448/s 7% --
...so it looks like keys generally wins - because of the
'random' order that things come out, you can't tell how
soon a loop test break you out of the loop.