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by SeanLuke 4316 days ago
> Backward compatibility in a RNG is actually rather important, weirdly enough. For example, anything that uses deterministic seeds for repeatability of procedural generation or optimization. (Read: Minecraft, among other more important things).

This seems like a very, very bad thing to rely on. Other than Java, how many other languages have guarantees in generator determinism from version to version as part of the language contract? Certainly Lisp considers it an antipattern.
2 comments
michaelt 4316 days ago
Any language that allows the PRNG to be manually seeded, presumably?

I mean, if manually seeding the PRNG doesn't produce a deterministic result, you wouldn't make it part of the API.

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SeanLuke 4316 days ago
Nope.

Essentially all languages allow manual seeding: almost none specify guarantees with regard to RNG behavior. I'm pretty sure this is because determinism of a given process important (everyone who does simulation needs that), but locking into potentially bad RNGs for the language or library itself, in fact specifying them, is a really bad idea.

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TheLoneWolfling 4315 days ago
Counterexample: Python [1]

[1] http://stackoverflow.com/a/19179886/1814881

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TheLoneWolfling 4316 days ago
If it's specified, I don't mind people relying on it. That being said, Java is over-specified in many ways, this potentially being one of them.

I know Python does not have this guarantee.

Personally? There should really be a couple different RNGs in Java's standard library - all combinations that make sense of [insecure/secure, can set seed / can't set seed, thread-local/global] (local/global being without distinction if one cannot set the seed). The default being secure / can't set seed.

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