Add Gen::fill method

This allows users to fairly easily migrate from CoreRng::fill_byte() and
similar constructions without requiring them to fuss around with a new
SeedableRng (or copy-paste this boilerplate) when their slice is just
full of Arbitrary-able types.

Signed-off-by: Aleksa Sarai <[email protected]>

src/arbitrary.rs

@@ -64,6 +64,16 @@ impl Gen {
         slice.choose(&mut self.rng)
     }
 
+    /// Fill a mutable slice of any Arbitrary-compatible type with Arbitrary
+    /// values.
+    pub fn fill<S, T>(&mut self, mut slice: S)
+    where
+        T: Arbitrary,
+        S: AsMut<[T]>,
+    {
+        slice.as_mut().fill_with(|| T::arbitrary(self))
+    }
+
     fn gen<T>(&mut self) -> T
     where
         rand::distributions::Standard: rand::distributions::Distribution<T>,