Add enum_u8 macro to simplify enum conversion

We need several enums that map to a u8 value.  This patch adds the
enum_u8 macro that automatically derives the From and TryFrom macros for
an enum to make these conversions easier.

As TryFrom is not stable yet, we add our own TryFrom trait.

1 files changed, 11 insertions, 21 deletions

diff --git a/src/hid.rs b/src/hid.rs
index 4f1d506..6274e7f 100644
--- a/src/hid.rs
+++ b/src/hid.rs
@@ -11,30 +11,20 @@ use usb_device::Result;
 
 const INTERFACE_CLASS_HID: u8 = 0x03;
 
-#[derive(Clone, Copy, Debug, PartialEq)]
-#[repr(u8)]
-pub enum Subclass {
-    None = 0x00,
-    BootInterface = 0x01,
-}
-
-impl From<Subclass> for u8 {
-    fn from(subclass: Subclass) -> u8 {
-        subclass as u8
+enum_u8! {
+    #[derive(Clone, Copy, Debug, PartialEq)]
+    pub enum Subclass {
+        None = 0x00,
+        BootInterface = 0x01,
     }
 }
 
-#[derive(Clone, Copy, Debug, PartialEq)]
-#[repr(u8)]
-pub enum Protocol {
-    None = 0x00,
-    Keyboard = 0x01,
-    Mouse = 0x02,
-}
-
-impl From<Protocol> for u8 {
-    fn from(protocol: Protocol) -> u8 {
-        protocol as u8
+enum_u8! {
+    #[derive(Clone, Copy, Debug, PartialEq)]
+    pub enum Protocol {
+        None = 0x00,
+        Keyboard = 0x01,
+        Mouse = 0x02,
     }
 }