[Issue 7067] New: std.random.RandomSample and RandomCover are poorly designed

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=7067

           Summary: std.random.RandomSample and RandomCover are poorly
                    designed
           Product: D
           Version: D2
          Platform: Other
        OS/Version: Windows
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Phobos
        AssignedTo: nobody at puremagic.com
        ReportedBy: thecybershadow at gmail.com
                CC: andrei at metalanguage.com


--- Comment #0 from Vladimir Panteleev <thecybershadow at 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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