4th digital::IoPin proposal from #29

src/digital.rs

@@ -24,3 +24,27 @@ pub trait InputPin {
     /// Is the input pin low?
     fn is_low(&self) -> bool;
 }
+
+/// Pins that can switch between input and output modes at runtime
+#[cfg(feature = "unproven")]
+pub trait IoPin {
+    /// Used by [`into_input()`](#tymethod.into_input)
+    ///
+    /// In addition to being an [`InputPin`](trait.InputPin.html), the
+    /// target type must implement `IoPin` so that the mode can be
+    /// changed again.
+    type Input: InputPin + IoPin<Input = Self::Input, Output = Self::Output>;
+
+    /// Used by [`into_output()`](#tymethod.into_output)
+    ///
+    /// In addition to being an [`OutputPin`](trait.OutputPin.html),
+    /// the target type must implement `IoPin` so that the mode can be
+    /// changed again.
+    type Output: OutputPin + IoPin<Input = Self::Input, Output = Self::Output>;
+
+    /// Configure as [`InputPin`](trait.InputPin.html)
+    fn into_input(self) -> Self::Input;
+
+    /// Configure as [`OutputPin`](trait.OutputPin.html)
+    fn into_output(self) -> Self::Output;
+}