[swift-evolution] [Proposal] Random Unification

[Kevin Nattinger]

IMO, we should have a `Random` or `RandomGenerator` interface and the stdlib can provide a `SystemRandom` that wraps arc4*/random(), and maybe a cryptographically secure one too (MT19937?).

protocol RandomGenerator {
    func uniform() -> Int
    func uniform() -> Double
    func uniformBytes(count: Int) -> Data
}

Then we could add things like, e.g. a protocol extension to generate normally distributed numbers (https://en.wikipedia.org/wiki/Box%E2%80%93Muller_transform <https://en.wikipedia.org/wiki/Box%E2%80%93Muller_transform>).

extension RandomGenerator {
    func normal<T: FloatingPoint>() -> (T, T) {
        // ...
    }
}

> On Sep 8, 2017, at 10:08 AM, Shawn Erickson via swift-evolution <swift-evolution at swift.org> wrote:
> 
> It would be nice to leverage range support instead of a start and end value IMHO.
> On Fri, Sep 8, 2017 at 9:52 AM Alejandro Alonso via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
> Hello swift evolution, I would like to propose a unified approach to `random()` in Swift. I have a simple implementation here https://gist.github.com/Azoy/5d294148c8b97d20b96ee64f434bb4f5 <https://gist.github.com/Azoy/5d294148c8b97d20b96ee64f434bb4f5>. This implementation is a simple wrapper over existing random functions so existing code bases will not be affected. Also, this approach introduces a new random feature for Linux users that give them access to upper bounds, as well as a lower bound for both Glibc and Darwin users. This change would be implemented within Foundation.
> 
> I believe this simple change could have a very positive impact on new developers learning Swift and experienced developers being able to write single random declarations.
> 
> I’d like to hear about your ideas on this proposal, or any implementation changes if need be.
> 
> - Alejando
> 
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