Seedable RNG and separation/extension of .gen_* functions

[Dretch]

There should be some sort of seedable implementation of rand::rng so that sequences of random operations can be easily reproduced.

The gen_* methods in the rand::rng iface should be separated out into an iface-less implementation for the rand::rng iface-type, i.e.:

impl gen for rng {
    fn gen_str (len: uint) -> str { ... }
    ....
}

This will allow multiple implementations of the rand::rng iface to use the gen_* methods.

There should be more gen_* methods available, for example:

• there should be one for each primitive integer/float type
• there should be shuffle-vector, choose-from-vector, choose-from-weighted-vector methods
• the functions from /src/fuzzer/rand_util.rs should become gen_methods

Motivation

I have been writing a fuzzer and I would have found these things useful to have in the core/std library.

[brson]

Yes, please.

[pcwalton]

Also useful for quickcheck (which is basically a fuzzer).

[Dretch]

Ok then, I would like to work on this. I will submit a pull request when i'm ready.

[eholk]

I'm closing this, since it looks like the code to do it is already in the tree.