Introduce sample and sample_iter into the Rng trait.

These traits take a reference to a `Distribution<T>` and generate values from that distribution.

src/lib.rs

@@ -237,6 +237,7 @@ use std::mem;
 use std::io;
 use std::rc::Rc;
 use std::num::wrapping::Wrapping as w;
+use std::num::Int;
 
 pub use os::OsRng;
 
@@ -416,6 +417,14 @@ pub trait Rng : Sized {
         Generator { rng: self, _marker: marker::PhantomData }
     }
 
+    fn sample<'a, T, D: Distribution<T>>(&'a mut self, distribution: &'a D) -> T {
+        distribution.sample(self)
+    }
+
+    fn sample_iter<'a, T, D: Distribution<T>>(&'a mut self, distribution: &'a D) -> SampleIter<'a, Self, D, T> {
+        SampleIter { rng: self, distribution: distribution, _marker: marker::PhantomData }
+    }
+
     /// Generate a random value in the range [`low`, `high`).
     ///
     /// This is a convenience wrapper around
@@ -535,6 +544,24 @@ impl<'a, T: Rand, R: Rng> Iterator for Generator<'a, T, R> {
     }
 }
 
+pub struct SampleIter<'a, R:'a, D:'a, T> {
+    rng: &'a mut R,
+    distribution: &'a D,
+    _marker: marker::PhantomData<fn() -> T>,
+}
+
+impl <'a, R: Rng, D: Distribution<T>, T> Iterator for SampleIter<'a, R, D, T> {
+    type Item = T;
+
+    fn next(&mut self) -> Option<T> {
+        Some(self.distribution.sample(self.rng))
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (Int::max_value(), None)
+    }
+}
+
 /// Iterator which will continuously generate random ascii characters.
 ///
 /// This iterator is created via the `gen_ascii_chars` method on `Rng`.