libcore: rand refactor & remove @'s from {rand,run}.rs

[huonw]

From a cursory git grep this removes the last part of core that requires on @ (other than io and the task local data section).

It renames RandRes to StdRng IsaacRng and XorShiftState to XorShiftRng as well as moving their constructors to static methods. To go with this, it adds rng() which is designed to be used when the programmer just wants a random number generator, without caring about which exact algorithm is being used.

It also removes all the gen_int, gen_uint, gen_char (etc) methods on RngUtil (by moving the defintions to the actual Rand instances). The replacement is using RngUtil::gen, either type-inferred or with an annotation (rng.gen::<uint>()).

I tried to have the Rng and RngUtil traits exported by core::prelude (since core::rand (except for random()) is useless without them), but this caused an explosion of (seemingly unrelated) error: unresolved import's.

[z0w0]

I feel like rand::IsaacRng would be a better name than StdRng.

[huonw]

That seems reasonable. (edit: done!)

[nikomatsakis]

r+ This looks good; we may also want to implement the trait Rng for the object type @Rng:

impl Rng for @Rng { pub fn next(&self) -> u32 { self.next() } }

so that people can use the object type should they choose to (sometimes it's more convenient).

[nikomatsakis]

Oh, I see you already did that, I missed it.