added opt-in default impl for spi::transactional

Author: ryankurte

src/blocking/spi.rs

@@ -125,3 +125,32 @@ pub trait Transactional<W: 'static> {
     /// Execute the provided transactions
     fn exec<'a>(&mut self, operations: &mut [Operation<'a, W>]) -> Result<(), Self::Error>;
 }
+
+/// Blocking transactional impl over spi::Write and spi::Transfer
+pub mod transactional {
+    use super::{Operation, Transactional, Transfer, Write};
+
+    /// Default implementation of `blocking::spi::Transactional<W>` for implementers of
+    /// `spi::Write<W>` and `spi::Transfer<W>`
+    pub trait Default<W, E>: Transfer<W, Error=E> + Write<W, Error=E> {}
+
+    impl<W: 'static, E, S> Transactional<W> for S
+    where
+        S: Default<W, E> + Transfer<W, Error = E> + Write<W, Error = E>,
+        W: Clone,
+        E: core::fmt::Debug,
+    {
+        type Error = E;
+
+        fn exec<'a>(&mut self, operations: &mut [super::Operation<'a, W>]) -> Result<(), E> {
+            for op in operations {
+                match op {
+                    Operation::Write(w) => Write::write(self, w)?,
+                    Operation::Transfer(t) => Transfer::transfer(self, t).map(|_| ())?,
+                }
+            }
+
+            Ok(())
+        }
+    }
+}