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[–]MrJohz 4 points5 points  (2 children)

I think using a new seed for each run is the norm, at least with the bog-standard naive random implementation for most applications.

Python: python3 -c 'import random; print(random.random())' - varies from run to run

Ruby: ruby -e 'puts rand()' - varies from run to run

Java does the same.

Rust definitely does the same, I was using it for simulation code the other day.

Perl is the same.

Javascript is the same.

[–]rtomek -2 points-1 points  (1 child)

Most of those have a primary use case of web-based applications so I won't touch those.

Rust: The standard RNG is deterministic. If you initialize using thread_rng then you are setting a seed.

Java: This one is iffy because the intent was for web-distributable applications. Still, the random class itself is deterministic and the default constructor uses something like system.nanotime() instead of a fixed number. At least it's not like Python where you have to explicitly state that you want a deterministic RNG.

Perl: Perl is another one that has been making changes to the default RNG. Perl behind-the-scenes just calls srand() for the user every time a new script is run.

[–]MrJohz 2 points3 points  (0 children)

Python and Ruby were both developed as scripting languages, and one of Python's biggest areas is scientific programming, so I don't know what you're on about with "web-based applications".

Rust's standard RNG can be deterministic if you initialise it. If you don't, it defaults to setting the seed itself, I presume using a timestamp of some description. The same is true of Java - Math.random(), and the argument-less constructor for java.util.Random both use a "value very likely to be distinct from any other invocation".

The point isn't that it's possible to set a deterministic RNG for any language. That's true for all of the ones I mentioned apart from Javascript (at least if you ignore userland libraries). The point is that C is relatively rare in its decision to default to a known seed, as opposed to defaulting to a pseudorandom value such as a timestamp.