From ddd34824b79d1af1b40d6a01509842d0b4d648ea Mon Sep 17 00:00:00 2001
From: Robin Krahl <robin.krahl@ireas.org>
Date: Tue, 7 Jan 2020 13:07:15 +0000
Subject: Implement Default in the Enum! and Command! macros

For the transition to structopt, we have to be able to easily construct
enum variants once we have added fields to them.  Therefore we implement
the Default trait in the generated macros by choosing the first variant
as the default.
---
 src/arg_util.rs | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/src/arg_util.rs b/src/arg_util.rs
index 06a6ee6..d54dd94 100644
--- a/src/arg_util.rs
+++ b/src/arg_util.rs
@@ -76,6 +76,8 @@ macro_rules! Command {
         }
       }
     }
+
+    impl_default!($name => $( $name::$var(::std::default::Default::default()) , )*);
   };
   ( $name:ident, [ $( $var:ident => ($str:expr, $exec:expr), ) *] ) => {
     #[derive(Debug, PartialEq)]
@@ -128,6 +130,8 @@ macro_rules! Command {
         }
       }
     }
+
+    impl_default!($name => $( $name::$var , )*);
   };
 }
 
@@ -204,6 +208,19 @@ macro_rules! enum_int {
         }
       }
     }
+
+    impl_default!($name => $( $name::$var , )*);
+
+  };
+}
+
+macro_rules! impl_default {
+  ( $name:ident => $def:expr , $( $other:expr , ) *) => {
+    impl ::std::default::Default for $name {
+      fn default() -> Self {
+        $def
+      }
+    }
   };
 }
 
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