Summary: std.random.RandomSample and RandomCover are poorly
--- Comment #0 from Vladimir Panteleev <thecybersha...@gmail.com> 2011-12-05
04:00:22 PST ---
The following tests will always fail:
int a = [ 0, 1, 2, 3, 4, 5, 6, 7, 8 ];
assert(!equal(randomCover(a, rndGen()), randomCover(a, rndGen())));
assert(!equal(randomSample(a, 5, rndGen()), randomSample(a, 5, rndGen())));
The reason why these tests will fail is that both functions take the RNG by
value. Not only is this unintuitive, this is also a security liability -
someone depending on these functions to generate random identifiers can be
surprised that two successive calls generate the same ID.
I strongly suggest that RNG types are disallowed from being implicitly copied.
Even though pseudo-random number generators shouldn't be used for security
purposes, they're still likely to be used in such contexts - especially
considering lack of better sources of random data in Phobos.
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