feat(macros): arg_enum! and simple_enum! auto-implement Display

enums created with simple_enum! and arg_enum! now auto-implement
std::fmt::Display where the variant only is displayed.

Closes #120

Author: kbknapp

src/macros.rs

@@ -277,6 +277,8 @@ macro_rules! value_t_or_exit {
 /// Convenience macro generated a simple enum with variants to be used as a type when parsing
 /// arguments.
 ///
+/// **NOTE:** This macro automaically implements std::str::FromStr and std::fmt::Display
+///
 /// # Example
 ///
 /// ```no_run
@@ -322,6 +324,14 @@ macro_rules! simple_enum {
                 }
             }
         }
+
+        impl ::std::fmt::Display for $e {
+            fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
+                match *self {
+                    $($e::$v => write!(f, stringify!($v)),)+
+                }
+            }
+        }
     };
 }
 
@@ -330,6 +340,8 @@ macro_rules! simple_enum {
 ///
 /// **NOTE:** Case insensitivity is supported for ASCII characters
 ///
+/// **NOTE:** This macro automaically implements std::str::FromStr and std::fmt::Display
+///
 /// These enums support pub (or not) and use of the #[derive()] traits
 ///
 ///
@@ -385,6 +397,14 @@ macro_rules! arg_enum {
                 }
             }
         }
+
+        impl ::std::fmt::Display for $e {
+            fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
+                match *self {
+                    $($e::$v => write!(f, stringify!($v)),)+
+                }
+            }
+        }
     };
     (pub enum $e:ident { $($v:ident),+ } ) => {
         pub enum $e {
@@ -411,6 +431,14 @@ macro_rules! arg_enum {
                 }
             }
         }
+
+        impl ::std::fmt::Display for $e {
+            fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
+                match *self {
+                    $($e::$v => write!(f, stringify!($v)),)+
+                }
+            }
+        }
     };
     (#[derive($($d:ident),+)] enum $e:ident { $($v:ident),+ } ) => {
         #[derive($($d,)+)]
@@ -438,6 +466,14 @@ macro_rules! arg_enum {
                 }
             }
         }
+
+        impl ::std::fmt::Display for $e {
+            fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
+                match *self {
+                    $($e::$v => write!(f, stringify!($v)),)+
+                }
+            }
+        }
     };
     (#[derive($($d:ident),+)] pub enum $e:ident { $($v:ident),+ } ) => {
         #[derive($($d,)+)]
@@ -465,6 +501,14 @@ macro_rules! arg_enum {
                 }
             }
         }
+
+        impl ::std::fmt::Display for $e {
+            fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
+                match *self {
+                    $($e::$v => write!(f, stringify!($v)),)+
+                }
+            }
+        }
     };
 }