Simplify beep example

examples/beep.rs

@@ -1,38 +1,18 @@
 extern crate cpal;
 
-// TODO: manual replacement for unstable `std::iter::iterate`
-struct Iter {
-    value: f32,
-}
-
-impl Iterator for Iter {
-    type Item = f32;
-
-    fn next(&mut self) -> Option<f32> {
-        self.value += 0.03;
-        Some(self.value)
-    }
-}
-
 fn main() {
     let mut channel = cpal::Voice::new();
 
-    // producing a sinusoid
-    let mut data_source = Iter { value: 0.0 }
-            .map(|angle| {
-                let angle = angle.sin();
-
-                let max: u16 = std::u16::MAX;
-                let value = (max as f32 / 2.0) + (angle * (max as f32 / 2.0));
-                value as u16
-            });
+    // Produce a sinusoid of maximum amplitude.
+    let max = std::u16::MAX as f32;
+    let mut data_source = (0u64..).map(|t| t as f32 * 0.03)
+                                  .map(|t| ((t.sin() * 0.5 + 0.5) * max) as u16);
 
     loop {
         {
             let mut buffer = channel.append_data(1, cpal::SamplesRate(44100), 32768);
 
-            for sample in buffer.iter_mut() {
-                let value = data_source.next().unwrap();
+            for (sample, value) in buffer.iter_mut().zip(&mut data_source) {
                 *sample = value;
             }
         }